parallel (operator)

{{Short description|Mathematical operation modeling parallel resistors}}

{{about|a mathematical function modeling parallel resistors|other uses|Parallel (disambiguation)}}

The parallel operator $\|$ (pronounced "parallel", following the parallel lines notation from geometry; also known as reduced sum, parallel sum or parallel addition) is a binary operation which is used as a shorthand in electrical engineering, but is also used in kinetics, fluid mechanics and financial mathematics. The name parallel comes from the use of the operator computing the combined resistance of resistors in parallel.

Overview

The parallel operator represents the reciprocal value of a sum of reciprocal values (sometimes also referred to as the "reciprocal formula" or "harmonic sum") and is defined by:

: $a \parallel b \mathrel{:=} \frac{1}{\dfrac{1}{a} + \dfrac{1}{b}} = \frac{ab}{a + b},$

where {{mvar|a}}, {{mvar|b}}, and $a \parallel b$ are elements of the extended complex numbers $\overline{\mathbb{C}} = \mathbb{C}\cup\{ \infty\}.$ {{Wikibooks-inline|Associative Composition Algebra/Homographies}}

The operator gives half of the harmonic mean of two numbers a and b.

As a special case, for any number $a \in \overline{\mathbb{C}}$ :

: $a \parallel a = \frac1{2/a} = \tfrac12a.$

Further, for all distinct numbers {{nobr| $a \neq b$ :}}

: $\big| \,a \parallel b \,\big| > \tfrac12 \min\bigl(|a|, |b|\bigr),$

with $\big|\, a \parallel b \,\big|$ representing the absolute value of $a \parallel b$ , and $\min(x, y)$ meaning the minimum (least element) among {{mvar|x}} and {{mvar|y}}.

If $a$ and $b$ are distinct positive real numbers then $\tfrac12 \min(a, b) < \big|\, a \parallel b \,\big| < \min(a, b).$

The concept has been extended from a scalar operation to matrices and further generalized.

Notation

The operator was originally introduced as reduced sum by Sundaram Seshu in 1956, studied as operator ∗ by Kent E. Erickson in 1959, and popularized by Richard James Duffin and William Niles Anderson, Jr. as parallel addition or parallel sum operator : in mathematics and network theory since 1966. While some authors continue to use this symbol up to the present, for example, Sujit Kumar Mitra used ∙ as a symbol in 1970. In applied electronics, a ∥ sign became more common as the operator's symbol around 1974. This was often written as doubled vertical line ({{!}}{{!}}) available in most character sets (sometimes italicized as //), but now can be represented using Unicode character U+2225 ( ∥ ) for "parallel to". In LaTeX and related markup languages, the macros \| and \parallel are often used (and rarely \smallparallel is used) to denote the operator's symbol.

Properties

Let $\widetilde{\C}$ represent the extended complex plane excluding zero, $\widetilde{\C} := \C \cup \{\infty\} \smallsetminus \{0\},$ and $\varphi$ the bijective function from $\C$ to $\widetilde{\C}$ such that $\varphi(z)=1/z.$ One has identities

: $\varphi(zt)=\varphi(z)\varphi(t),$

and

: $\varphi(z+t)=\varphi(z)\parallel \varphi(t)$

This implies immediately that $\widetilde{\C}$ is a field where the parallel operator takes the place of the addition, and that this field is isomorphic to $\C.$

The following properties may be obtained by translating through $\varphi$ the corresponding properties of the complex numbers.

= Field properties =

As for any field, $(\widetilde{\C}, \,\parallel\,, \,\cdot\,)$ satisfies a variety of basic identities.

It is commutative under parallel and multiplication:

: $\begin{align}
a \parallel b &= b \parallel a \\[3mu]
ab &= ba
\end{align}$

It is associative under parallel and multiplication:

: $\begin{align}
&(a \parallel b) \parallel c = a \parallel (b \parallel c) = a \parallel b \parallel c
= \frac{1}{\dfrac{1}{a} + \dfrac{1}{b} + \dfrac{1}{c}} = \frac{a b c}{a b + a c + b c}, \\
&(ab) c = a (b c) = a b c.
\end{align}$

Both operations have an identity element; for parallel the identity is $\infty$ while for multiplication the identity is {{math|1}}:

: $\begin{align}
&a \parallel \infty = \infty \parallel a = \frac1{\dfrac1a + 0} = a, \\
&1 \cdot a = a \cdot 1 = a.
\end{align}$

Every element $a$ of $\widetilde{\C}$ has an inverse under parallel, equal to $-a,$ the additive inverse under addition. (But {{math|0}} has no inverse under parallel.)

: $a \parallel (-a) = \frac1{\dfrac1a - \dfrac1a} = \infty.$

The identity element $\infty$ is its own inverse, $\infty \parallel \infty = \infty.$

Every element $a \neq \infty$ of $\widetilde{\C}$ has a multiplicative inverse {{nobr| $a^{-1} = 1/a$ :}}

: $a\cdot\frac1a = 1.$

Multiplication is distributive over parallel:

: $k (a \parallel b) = \frac{k}{\dfrac1a + \dfrac1b} = \frac{1}{\dfrac1{ka} + \dfrac1{kb}} = ka \parallel kb.$

= Repeated parallel =

Repeated parallel is equivalent to division,

: $\underbrace{a \parallel a \parallel \cdots \parallel a}_{n\text{ times}}
= \frac1{\underbrace{\dfrac1a + \dfrac1a + \cdots + \dfrac1a}_{n\text{ times}}} = \frac an.$

Or, multiplying both sides by {{mvar|n}},

: $n (\underbrace{a \parallel a \parallel \cdots \parallel a}_{n\text{ times}}) = a.$

Unlike for repeated addition, this does not commute:

: $\frac ab \neq \frac ba \quad \text{implies}\quad
\underbrace{a \parallel a \parallel \cdots \parallel a}_{b\text{ times}} \,\neq\, \underbrace{b \parallel b \parallel \cdots \parallel b}_{a\text{ times}}~\!.$

= Binomial expansion =

Using the distributive property twice, the product of two parallel binomials can be expanded as

: $\begin{align}
(a \parallel b) (c \parallel d)
&= a(c \parallel d) \parallel b(c \parallel d) \\[3mu]
&= ac \parallel ad \parallel bc \parallel bd.
\end{align}$

The square of a binomial is

: $\begin{align}
(a \parallel b)^2
&= a^2 \parallel ab \parallel ba \parallel b^2 \\[3mu]
&= a^2 \parallel \tfrac12ab \parallel b^2.
\end{align}$

The cube of a binomial is

: $(a \parallel b)^3 = a^3 \parallel \tfrac13a^2b \parallel \tfrac13ab^2 \parallel b^3.$

In general, the {{mvar|n}}th power of a binomial can be expanded using binomial coefficients which are the reciprocal of those under addition, resulting in an analog of the binomial formula:

: $(a \parallel b)^n = \frac{a^n}{\binom n0} \parallel \frac{a^{n-1}b}{\binom n1} \parallel \cdots \parallel \frac{a^{n-k}b^k}{\binom nk} \parallel \cdots \parallel \frac{b^n}{\binom nn}.$

= Logarithm and exponential =

The following identities hold:

: $\frac{1}{\log(ab)} = \frac{1}{\log(a)}\parallel\frac{1}{\log(b)},$

: $\exp\left(\frac{1}{a\parallel b}\right) = \exp\left(\frac{1}{a}\right)\exp\left(\frac{1}{b}\right)$

= Factoring parallel polynomials =

As with a polynomial under addition, a parallel polynomial with coefficients $a_k$ in $\widetilde\C$ (with {{nobr| $a_0 \neq \infty$ )}} can be factored into a product of monomials:

: $\begin{align}
&a_0x^n \parallel a_1x^{n-1} \parallel \cdots \parallel a_n =a_0(x \parallel -r_1)(x \parallel -r_2)\cdots(x \parallel -r_n)
\end{align}$

for some roots $r_k$ (possibly repeated) in $\widetilde\C.$

Analogous to polynomials under addition, the polynomial equation

: $(x \parallel -r_1)(x \parallel -r_2)\cdots(x \parallel -r_n) = \infty$

implies that $x = r_k$ for some {{mvar|k}}.

= Quadratic formula =

A linear equation can be easily solved via the parallel inverse:

: $\begin{align}
ax\parallel b &= \infty \\[3mu]
\implies x &= -\frac ba.
\end{align}$

To solve a parallel quadratic equation, complete the square to obtain an analog of the quadratic formula

: $\begin{align}
ax^2\parallel bx \parallel c &= \infty \\[5mu]
x^2\parallel \frac{b}{a}x &= - \frac{c}{a} \\[5mu]
x^2\parallel \frac{b}{a}x\parallel \frac{4b^2}{a^2} &= \left(-\frac{c}{a}\right) \parallel \frac{4b^2}{a^2} \\[5mu]
\left(x\parallel \frac{2b}{a}\right)^2 &= \frac{b^2 \parallel -\tfrac14ac}{\tfrac14a^2} \\[5mu]
\implies x &= \frac{(-b) \parallel \pm\sqrt{b^2 \parallel -\tfrac14ac} }{\tfrac12a}.
\end{align}$

= Including zero =

The extended complex numbers including zero, $\overline{\mathbb{C}} := \C \cup \infty,$ is no longer a field under parallel and multiplication, because {{math|0}} has no inverse under parallel. (This is analogous to the way $\bigl(\overline{\mathbb{C}}, {+}, {\cdot} \bigr)$ is not a field because $\infty$ has no additive inverse.)

For every non-zero {{mvar|a}},

: $a \parallel 0 = \frac1{\dfrac1a + \dfrac10} = 0$

The quantity $0 \parallel (-0) = 0 \parallel 0$ can either be left undefined (see indeterminate form) or defined to equal {{math|0}}.

= Precedence =

In the absence of parentheses, the parallel operator is defined as taking precedence over addition or subtraction, similar to multiplication.

Applications

There are applications of the parallel operator in mechanics, electronics, optics, and study of periodicity:

=Reduced mass=

Given masses m and M, the reduced mass $\mu = \frac{m M}{m + M} = m \parallel M$ is frequently applied in mechanics. For instance, when the masses orbit each other, the moment of inertia is their reduced mass times the distance between them.

= Circuit analysis =

In electrical engineering, the parallel operator can be used to calculate the total impedance of various serial and parallel electrical circuits.

There is a duality between the usual (series) sum and the parallel sum.

For instance, the total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors.

:A diagram of several resistors, side by side, both leads of each connected to the same wires.

: $\begin{align}
\frac{1}{R_\text{eq}} &= \frac{1}{R_1} + \frac{1}{R_2} + \cdots + \frac{1}{R_n} \\[5mu]
R_\text{eq} &= R_1 \parallel R_2 \parallel \cdots \parallel R_n.
\end{align}$

Likewise for the total capacitance of serial capacitors.

= Coalescence of independent probability density functions. =

The coalesced density function f_coalesced(x) of n independent probability density functions f₁(x), f₂(x), …, f_n(x), is equal to the reciprocal of the sum of the reciprocal densities.Van Droogenbroeck, Frans J., [https://www.academia.edu/127477986/ 'Coalescence, unlocking insights in the intricacies of merging independent probability density functions'] (2025).

: $\begin{align}
\frac{1}{f_{coalesced}(x)} &= \frac{1}{f_1(x)} + \frac{1}{f_2(x)} + \cdots + \frac{1}{f_n(x)} \\[5mu]
\end{align}$

= Lens equation =

In geometric optics the thin lens approximation to the lens maker's equation.

: $f = \rho_{virtual}\parallel \rho_{object}$

=Synodic period=

The time between conjunctions of two orbiting bodies is called the synodic period. If the period of the slower body is T₂, and the period of the faster is T₁, then the synodic period is

: $T_{syn} = T_1 \parallel (-T_2) .$

Examples

Question:

: Three resistors $R_1 = 270\,\mathrm{k\Omega}$ , $R_2 = 180\,\mathrm{k\Omega}$ and $R_3 = 120\,\mathrm{k\Omega}$ are connected in parallel. What is their resulting resistance?

Answer:

: $\begin{align}
R_1 \parallel R_2 \parallel R_3 &= 270\,\mathrm{k\Omega} \parallel 180\,\mathrm{k\Omega} \parallel 120\,\mathrm{k\Omega} \\[5mu]
&= \frac{1}{\dfrac{1}{270\,\mathrm{k\Omega}} + \dfrac{1}{180\,\mathrm{k\Omega}} + \dfrac{1}{120\,\mathrm{k\Omega}}} \\[5mu]
&\approx 56.84 \,\mathrm{k\Omega}
\end{align}$

: The effectively resulting resistance is ca. 57 kΩ.

Question:

: A construction worker raises a wall in 5 hours. Another worker would need 7 hours for the same work. How long does it take to build the wall if both workers work in parallel?

Answer:

: $t_1 \parallel t_2 = 5\,\mathrm h \parallel 7\,\mathrm h = \frac{1}{\dfrac{1}{5\,\mathrm h} + \dfrac{1}{7\,\mathrm h}} \approx 2.92\,\mathrm h$

: They will finish in close to 3 hours.

Implementation

File:Hp30bwp34s.jpg with parallel operator (∥) on the {{keypress|g|÷}} key.]]

Suggested already by Kent E. Erickson as a subroutine in digital computers in 1959, the parallel operator is implemented as a keyboard operator on the Reverse Polish Notation (RPN) scientific calculators WP 34S since 2008 as well as on the WP 34C and WP 43S since 2015, allowing to solve even cascaded problems with few keystrokes like {{keypress|270}}{{keypress|ENTER}}{{keypress|180}}{{keypress|∥}}{{keypress|120}}{{keypress|∥}}.

Projective view

Given a field F there are two embeddings of F into the projective line P(F): z → [z : 1] and z → [1 : z]. These embeddings overlap except for [0:1] and [1:0]. The parallel operator relates the addition operation between the embeddings. In fact, the homographies on the projective line are represented by 2 x 2 matrices M(2,F), and the field operations (+ and ×) are extended to homographies. Each embedding has its addition a + b represented by the following matrix multiplications in M(2,A):

: $\begin{align}
\begin{pmatrix} 1 & 0 \\ a & 1 \end{pmatrix} \begin{pmatrix} 1 & 0 \\ b & 1 \end{pmatrix}
&= \begin{pmatrix} 1 & 0 \\ a+b & 1 \end{pmatrix},
\\[10mu]
\begin{pmatrix} 1 & a \\ 0 & 1 \end{pmatrix} \begin{pmatrix} 1 & b \\ 0 & 1 \end{pmatrix}
&= \begin{pmatrix} 1 & a+b \\ 0 & 1 \end{pmatrix}.
\end{align}$

The two matrix products show that there are two subgroups of M(2,F) isomorphic to (F,+), the additive group of F. Depending on which embedding is used, one operation is +, the other is $\parallel.$

Notes

{{Reflist|group="nb"|refs=

While the use of the symbol ∥ for "parallel" in geometry reaches as far back as 1673 in John Kersey the elder's work,{{citeref|Kersey_(the_elder)|1673|A}} this came into more use only since about 1875.{{citeref|Cajori|1993|B}} The usage of a mathematical operator for parallel circuits originates from network theory in electrical engineering. Sundaram Seshu introduced a reduced sum operator in 1956,{{citeref|Seshu|1956|C}} Kent E. Erickson proposed an asterisk (∗) to symbolize the operator in 1959,{{citeref|Erickson|1959|D}} whilst Richard James Duffin and William Niles Anderson, Jr. used a colon (:) for the parallel addition since 1966.{{citeref|Duffin|Hazony|Morrison|1966|E}} Sujit Kumar Mitra used a middot (∙) for it in 1970.{{citeref|Mitra|1970|F}} The first usage of the parallel symbol (∥) for this operator in applied electronics is unknown, but might have originated from {{ill|Stephen D. Senturia|d|Q94138984}} and Bruce D. Wedlock's 1974 book "Electronic Circuits and Applications",{{citeref|Senturia|Wedlock|1975|G}} which evolved from their introductory electronics course at Massachusetts Institute of Technology (MIT) with concepts of teaching network theory and electronics derived from an earlier course taught by Campbell "Cam" Leach Searle. It was further popularized through John W. McWane's 1981 book "Introduction to Electronics and Instrumentation",{{citeref|McWane|1981|H}} which grew out of an identically-named MIT course developed as part of the influential {{citeref|Wiesner|Johnson|Killian, Jr.|1978|Technical Curriculum Development Project|style=plain}} between 1974 and 1979. This symbol was probably also introduced because the other used symbols could be easily confused with signs commonly used for multiplication and division in some contexts.

In electrical circuits the parallel operator can be applied to, respectively, parallel resistances (R in [Ω]) or inductances (L in [H]) as well as to impedances (Z in [Ω]) or reactances (X in [Ω]). Ignoring the operator symbol's then-misleading glyph it can also be applied to series circuits of, respectively, conductances (G in [S]) or capacitances (C in [F]) as well as to admittances (Y in [S]) or susceptances (B in [S]).

}}

References

{{Reflist|refs=

{{cite book |author-first=John |author-last=Kersey (the elder) |author-link=John Kersey the elder |title=The Elements of that Mathematical Art, commonly called Algebra |location=London |date=1673 |volume=Book IV - The Elements of the Algebraical Arts |chapter=Chapter I: Concerning the Scope of this fourth Book and the Signification of Characters, Abbreviations and Citations used therein |publisher=Thomas Passinger, Three-Bibles, London-Bridge |pages=177–178 |url=https://archive.org/details/b30333726_0002 |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20200805135008/https://archive.org/details/b30333726_0002 |archive-date=2020-08-05}}

{{cite book |author-first=Florian |author-last=Cajori |author-link=Florian Cajori |title=A History of Mathematical Notations – Notations in Elementary Mathematics |chapter=§ 184, § 359, § 368 |volume=1 |orig-date=September 1928 |publisher=Open court publishing company |location=Chicago, US |date=1993 |edition=two volumes in one unaltered reprint |pages=[https://archive.org/details/historyofmathema00cajo_0/page/193 193, 402–403, 411–412] |isbn=0-486-67766-4 |lccn=93-29211 |url=https://archive.org/details/historyofmathema00cajo_0/page/193 |access-date=2019-07-22 |quote-pages=402–403, 411–412 |quote=§359. […] ∥ for parallel occurs in Oughtred's Opuscula mathematica hactenus inedita (1677) [p. 197], a posthumous work (§ 184) […] §368. Signs for parallel lines. […] when Recorde's sign of equality won its way upon the Continent, vertical lines came to be used for parallelism. We find ∥ for "parallel" in Kersey,{{citeref|A|ref=FC-A}} Caswell, Jones,{{citeref|B|ref=FC-B}} Wilson,{{citeref|C|ref=FC-C}} Emerson,{{citeref|D|ref=FC-D}} Kambly,{{citeref|E|ref=FC-E}} and the writers of the last fifty years who have been already quoted in connection with other pictographs. Before about 1875 it does not occur as often […] Hall and Stevens{{citeref|F|ref=FC-F}} use "par{{citeref|F|ref=FC-F}} or ∥" for parallel […] {{anchor|FC-A}}[A] John Kersey, {{citeref|Kersey (the elder)|1673|Algebra|style=plain}} (London, 1673), Book IV, p. 177. {{anchor|FC-B}}[B] W. Jones, Synopsis palmarioum matheseos (London, 1706). {{anchor|FC-C}}[C] John Wilson, Trigonometry (Edinburgh, 1714), characters explained. {{anchor|FC-D}}[D] W. Emerson, Elements of Geometry (London, 1763), p. 4. {{anchor|FC-E}}[E] {{ill|Ludwig Kambly{{!}}L. Kambly|de|Ludwig Kambly}}, Die Elementar-Mathematik, Part 2: Planimetrie, 43. edition (Breslau, 1876), p. 8. […] {{anchor|FC-F}}[F] H. S. Hall and F. H. Stevens, Euclid's Elements, Parts I and II (London, 1889), p. 10. […]}} [https://monoskop.org/images/2/21/Cajori_Florian_A_History_of_Mathematical_Notations_2_Vols.pdf]

{{cite journal |title=On Electrical Circuits and Switching Circuits |date=September 1956 |author-first=Sundaram |author-last=Seshu |journal=IRE Transactions on Circuit Theory |volume=CT-3 |issue=3 |publisher=Institute of Radio Engineers (IRE) |pages=172–178 |doi=10.1109/TCT.1956.1086310 |url=https://www.researchgate.net/publication/3440524_On_Electrical_Circuits_and_Switching_Circuits}} (7 pages) (NB. See {{citeref|Seshu|Gould|1957|errata|style=plain}}.)

{{cite journal |title=Correction to 'On Electrical Circuits and Switching Circuits' |series=Correction |date=September 1957 |author-first1=Sundaram |author-last1=Seshu |author-first2=Roderick |author-last2=Gould |journal=IRE Transactions on Circuit Theory |volume=CT-4 |issue=3 |publisher=Institute of Radio Engineers (IRE) |page=284 |doi=10.1109/TCT.1957.1086390 |url=https://www.researchgate.net/publication/3440591_Correction_to_'On_Electric_Circuits_and_Switching_Circuits'|doi-access=free }} (1 page) (NB. Refers to {{citeref|Seshu|1956|previous|style=plain}} reference.)

{{cite journal |author-first=Kent E. |author-last=Erickson |title=A New Operation for Analyzing Series-Parallel Networks |journal=IRE Transactions on Circuit Theory |volume=CT-6 |issue=1 |date=March 1959 |publisher=Institute of Radio Engineers (IRE) |doi=10.1109/TCT.1959.1086519 |pages=124–126 |url=https://www.researchgate.net/publication/3440722_A_New_Operation_for_Analyzing_Series-Parallel_Networks |quote-page=124 |quote=[…] The operation ∗ is defined as A ∗ B = AB/A + B. The symbol ∗ has algebraic properties which simplify the formal solution of many series-parallel network problems. If the operation ∗ were included as a subroutine in a digital computer, it could simplify the programming of certain network calculations. […]}} (3 pages) (NB. See {{citeref|Kaufman|1963|comment|style=plain}}.)

{{cite journal |author-first=Howard |author-last=Kaufman |title=Remark on a New Operation for Analyzing Series-Parallel Networks |journal=IEEE Transactions on Circuit Theory |volume=CT-10 |issue=2 |date=June 1963 |publisher=Institute of Electrical and Electronics Engineers (IEEE) |doi=10.1109/TCT.1963.1082126 |page=283 |quote-page=283 |quote=[…] Comments on the operation ∗ […] a∗b = ab/(a+b) […]}} (1 page) (NB. Refers to {{citeref|Erickson|1959|previous|style=plain}} reference.)

{{cite journal |title=Network synthesis through hybrid matrices |author-last1=Duffin |author-first1=Richard James |author-link1=Richard James Duffin |author-first2=Dov |author-last2=Hazony |author-first3=Norman Alexander |author-last3=Morrison |journal=SIAM Journal on Applied Mathematics |publisher=Society for Industrial and Applied Mathematics (SIAM) |volume=14 |number=2 |date=March 1966 |orig-date=1965-04-12, 1964-08-25 |pages=390–413 |jstor=2946272 |doi=10.1137/0114032}} (24 pages)

{{cite journal |author-last1=Anderson, Jr. |author-first1=William Niles |author-last2=Duffin |author-first2=Richard James |author-link2=Richard James Duffin |title=Series and parallel addition of matrices |journal=Journal of Mathematical Analysis and Applications |publisher=Academic Press, Inc. |volume=26 |issue=3 |pages=576–594 |date=1969 |orig-date=1968-05-27 |doi=10.1016/0022-247X(69)90200-5 |quote-page=576 |quote=[…] we define the parallel sum of A and B by the formula A(A + B)⁺B and denote it by A : B. If A and B are nonsingular this reduces to A : B = (A⁻¹ + B⁻¹)⁻¹ which is the well known electrical formula for addition of resistors in parallel. Then it is shown that the Hermitian semi-definite matrices form a commutative partially ordered semigroup under the parallel sum operation. […]|doi-access=free }} [https://kilthub.cmu.edu/articles/Series_and_parallel_addition_of_matrices/6479477/1]

{{cite journal |title=A Matrix Operation for Analyzing Series-parallel Multiports |journal=Journal of the Franklin Institute |publisher=Franklin Institute |series=Brief Communication |volume=289 |issue=2 |pages=167–169 |date=February 1970 |doi=10.1016/0016-0032(70)90302-9 |author-first=Sujit Kumar |author-last=Mitra |url=https://www.researchgate.net/publication/239368282_A_matrix_operation_for_analyzing_series-parallel_multiports |quote-page=167 |quote=The purpose of this communication is to extend the concept of the scalar operation Reduced Sum introduced by {{citeref|Seshu|1956|Seshu|style=plain}} […] and later elaborated by {{citeref|Erickson|1959|Erickson|style=plain}} […] to matrices, to outline some interesting properties of this new matrix operation, and to apply the matrix operation in the analysis of series and parallel n-port networks. Let A and B be two non-singular square matrices having inverses, A⁻¹ and B⁻¹ respectively. We define the operation ∙ as A ∙ B = (A⁻¹ + B⁻¹)⁻¹ and the operation ⊙ as A ⊙ B = A ∙ (−B). The operation ∙ is commutative and associative and is also distributive with respect to multiplication. […]}} (3 pages)

{{cite book |title=Mathematical Aspects of Electrical Network Analysis |series=Proceedings of a Symposium in Applied Mathematics of the American Mathematical Society and the Society for Industrial and Applied Mathematics held in New York City, 1969-04-02/03 |chapter=Network Models |pages=65–92 [68] |volume=III of SIAM-AMS Proceedings |date=1971 |orig-date=1970, 1969 |publisher=American Mathematical Society (AMS) / Society for Industrial and Applied Mathematics (SIAM) |edition=illustrated |publication-place=Providence, Rhode Island |editor-first1=Herbert Saul |editor-last1=Wilf |editor-link1=Herbert Saul Wilf |editor-first2=Frank |editor-last2=Hararay |editor-link2=Frank Harary |author-first=Richard James |author-last=Duffin |author-link=Richard James Duffin |location=Durham, North Carolina, USA |issn=0080-5084 |isbn=0-8218-1322-6 |id={{ISBN|978-0-8218-1322-5}}. Report 69-21 |lccn=79-167683 |chapter-url=https://books.google.com/books?id=j2vFhxA5K-UC&pg=PA65 |url=https://books.google.com/books?id=j2vFhxA5K-UC |access-date=2019-08-05 |quote-pages=68–69 |quote=[…] To have a convenient short notation for the joint resistance of resistors connected in parallel let […] A:B = AB/(A+B) […] A:B may be regarded as a new operation termed parallel addition […] Parallel addition is defined for any nonnegative numbers. The network model shows that parallel addition is commutative and associative. Moreover, multiplication is distributive over this operation. Consider now an algebraic expression in the operations (+) and (:) operating on positive numbers A, B, C, etc. […] To give a network interpretation of such a polynomial read A + B as "A series B" and A : B as "A parallel B" then it is clear that the expression […] is the joint resistance of the network […]}} [https://kilthub.cmu.edu/articles/Network_models/6478514] [https://kilthub.cmu.edu/ndownloader/files/11915081] (206 pages)

{{cite journal |title=On Parallel Sum and Difference of Matrices |journal=Journal of Mathematical Analysis and Applications |volume=44 |number=1 |pages=92–97 |date=October 1973 |doi=10.1016/0022-247X(73)90027-9 |author-first1=Sujit Kumar |author-last1=Mitra |author-first2=Madan Lal |author-last2=Puri |publisher=Academic Press, Inc. |url=https://core.ac.uk/download/pdf/82140285.pdf |archive-url=https://web.archive.org/web/20190413061307/https://core.ac.uk/download/pdf/82140285.pdf |archive-date=2019-04-13}}

{{cite book |title=Science and Engineering Technology – Curriculum Guide: A Guide to a Two-Year Associate Degree Curriculum |chapter=Section 4. Instructional Materials – 4.3. The MIT Technical Curriculum Development Project – Introduction to Electronics and Instrumentation |author-last=Wolf |author-first=Lawrence J. |editor-first1=Bill G. |editor-last1=Aldridge |editor-first2=Donald R. |editor-last2=Mowery |editor-first3=Lawrence J. |editor-last3=Wolf |editor-first4=Peggy |editor-last4=Dixon |location=Saint Louis Community College–Florissant Valley, St. Louis, Missouri, USA |date=1977 |orig-date=1976, 1974 |publisher=National Science Teachers Association, Washington DC, USA |pages=21, 77 |url=https://files.eric.ed.gov/fulltext/ED207786.pdf |access-date=2019-08-08 |url-status=live |archive-url=https://web.archive.org/web/20170215013912/http://files.eric.ed.gov/fulltext/ED207786.pdf |archive-date=2017-02-15 |quote-page=21 |quote=[…] {{citeref|Wiesner|Johnson|Killian, Jr.|1978|Introduction to Electronics and Instrumentation|style=plain}} is a new and contemporary approach to the introductory electronics course. Designed for students with no prior experience with electronics, it develops the skills and knowledge necessary to use and understand modern electronic systems. […] John W. McWane […]}} (NB. The SET Project was a two-year post-secondary curriculum developed between 1974 and 1977 preparing technicians to use electronic instruments.)

{{cite book |title=Report of the President and the Chancellor 1977–78 – Massachusetts Institute of Technology |chapter=School of Engineering – Center for Advanced Engineering Study (C.A.E.S.) – Research and Development – Technical Curriculum Research and Development Project |editor-first1=Jerome Bert |editor-last1=Wiesner |editor-link1=Jerome Bert Wiesner |editor-first2=Howard Wesley |editor-last2=Johnson |editor-link2=Howard Wesley Johnson |editor-first3=James Rhyne |editor-last3=Killian, Jr. |editor-link3=James Rhyne Killian |date=1978-04-11 |publisher=Massachusetts Institute of Technology (MIT) |pages=249, 252–253 |url=https://libraries.mit.edu/archives/mithistory/presidents-reports/1978.pdf |access-date=2019-08-08 |url-status=live |archive-url=https://web.archive.org/web/20150910145633/http://libraries.mit.edu/archives/mithistory/presidents-reports/1978.pdf |archive-date=2015-09-10 |quote-pages=249, 252–253 |quote=[…] The Technical Curriculum Research and Development Program, sponsored by the {{ill|Imperial Organization of Social Services|fa|سازمان شاهنشاهی خدمات اجتماعی}} of Iran, is entering the fourth year of a five-year contract. Curriculum development in electronics and mechanical engineering continues. […] Administered jointly by C.A.E.S. and the Department of Materials Science and Engineering, the Project is under the supervision of Professor Merton C. Flemings. It is directed by Dr. John W. McWane. […] Curriculum Materials Development. This is the principal activity of the project and is concerned with the development of innovative, state-of-the-art course materials in needed areas of engineering technology […] new introductory course in electronics […] is entitled Introduction to Electronics and Instrumentation and consists of eight […] modules […] dc Current, Voltage, and Resistance; Basic Circuit Networks; Time Varying Signals; Operational Amplifiers; Power Supplies; ac Current, Voltage, and Impedance; Digital Circuits; and Electronic Measurement and Control. This course represents a major change and updating of the way in which electronics is introduced, and should be of great value to STI as well as to many US programs. […]}}

{{cite book |title=Electronic Circuits and Applications |chapter=Part A. Learning the Language, Chapter 3. Linear Resistive Networks, 3.2 Basic Network Configurations, 3.2.3. Resistors in Parallel |date=1975 |orig-date=August 1974 |author-first=Stephen D. |author-last=Senturia |author-link=:d:Q94138984 |author-first2=Bruce D. |author-last2=Wedlock |location=Massachusetts Institute of Technology, Cambridge, Massachusetts, USA |publisher=John Wiley & Sons, Inc. |publication-place=New York, London, Sydney, Toronto |edition=1 |isbn=0-471-77630-0 |lccn=74-7404 |s2cid=61070327 |pages=viii–ix, 44–46 [45] |quote-pages=viii, ix, 45 |quote=This textbook evolved from a one-semester introductory electronics course taught by the authors at the Massachusetts Institute of Technology. […] The course is used by many freshmen as a precursor to the MIT Electrical Engineering Core Program. […] The preparation of a book of this size has drawn on the contribution of many people. The concept of teaching network theory and electronics as a single unified subject derives from Professor Campbell Searle, who taught the introductory electronics course when one of us (S.D.S.) was a first-year physics graduate student trying to learn electronics. In addition, Professor Searle has provided invaluable constructive criticism throughout the writing of this text. Several members of the MIT faculty and nearly 40 graduate technical assistants have participated in the teaching of this material over the past five years, many of whom have made important contributions through their suggestions and examples. Among these, we especially wish to thank O. R. Mitchell, Irvin Englander, George Lewis, Ernest Vincent, David James, Kenway Wong, Gim Hom, Tom Davis, James Kirtley, and Robert Donaghey. The chairman of the MIT Department of Electrical Engineering, Professor Louis D. Smullin, has provided support and encouragement during this project, as have many colleagues throughout the department. […] The first result […] states that the total voltage across the parallel combination of R₁ and R₂ is the same as that which occurs across a single resistance of value R₁ R₂ (R₁ + R₂). Because this expression for parallel resistance occurs so often, it is given a special notation (R₁∥R₂). That is, when R₁ and R₂ are in parallel, the equivalent resistance is $(R_1 \parallel R_2) = \frac{R_1 R_2}{R_1+R_2}$ […]}} (xii+623+5 pages) (NB. A teacher's manual was available as well. Early print runs contains a considerable number of typographical errors. See also: Wedlock's 1978 {{citeref|Wedlock|1978|book|style=plain}}.) [https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4321201]

{{cite book |title=Basic circuit networks |series=Introduction to electronics and instrumentation |date=1978 |author-first=Bruce D. |author-last=Wedlock |publisher=Massachusetts Institute of Technology (MIT), Technical Curriculum Research and Development Project }} (81 pages) (NB. This formed the basis for Part I of McWane's 1981 {{citeref|McWane|1981|book|style=plain}}. See also: Senturia's and Wedlock's 1975 {{citeref|Senturia|Wedlock|1975|book|style=plain}}.)

{{cite book |title=Introduction to Electronics and Instrumentation |author-first=John W. |author-last=McWane |date=1981-05-01 |edition=illustrated |publisher=Breton Publishers, Wadsworth, Inc. |location=North Scituate, Massachusetts, USA |isbn=0-53400938-7 |id={{ISBN|978-0-53400938-0}} |pages=78, 96–98, 100, 104 |url=https://books.google.com/books?id=NKy1nQ8Y_V0C |access-date=2019-08-04 |quote-page=xiii, 96–98, 100 |quote=[…] Bruce D. Wedlock […] was the principle contributing author to Part I, {{citeref|Wedlock|1978|BASIC CIRCUIT NETWORKS|style=plain}} including the design of the companion examples. […] Most of the development of the IEI program was undertaken as part of the {{citeref|Wiesner|Johnson|Killian, Jr.|1978|Technical Curriculum Research and Development Project|style=plain}} of the MIT Center of Advanced Engineering Study. […] shorthand notation […] shorthand symbol ∥ […]}} (xiii+545 pages) (NB. In 1981, a 216-pages laboratory manual accompanying this book existed as well. The work grew out of an MIT course program "{{citeref|Wiesner|Johnson|Killian, Jr.|1978|The MIT Technical Curriculum Development Project - Introduction to Electronics and Instrumentation|style=plain}}" developed between 1974 and 1979. In 1986, a second edition of this book was published under the title "Introduction to Electronics Technology".)

{{cite journal |author-last1=Eriksson-Bique |author-first1=Sirkka-Liisa Anneli |author-link1=:fi:Sirkka-Liisa Eriksson |author-last2=Leutwiler |author-first2=Heinz |title=A generalization of parallel addition |journal=Aequationes Mathematicae |publisher=Birkhäuser Verlag |date=February 1989 |orig-date=1989-01-10 |volume=38 |issue=1 |pages=99–110 |doi=10.1007/BF01839498 |url=https://link.springer.com/content/pdf/10.1007/BF01839498.pdf |access-date=2020-08-20 |url-status=live |archive-url=https://web.archive.org/web/20200820155352/https://link.springer.com/content/pdf/10.1007/BF01839498.pdf |archive-date=2020-08-20}}

{{cite book |title=Intellectual Trespassing as a Way of Life: Essays in Philosophy, Economics, and Mathematics |chapter=Chapter 12: Parallel Addition, Series-Parallel Duality, and Financial Mathematics |series=The worldly philosophy: studies in intersection of philosophy and economics |author-first=David Patterson |author-last=Ellerman |author-link=David Patterson Ellerman |edition=illustrated |publisher=Rowman & Littlefield Publishers, Inc. |date=1995-03-21 |isbn=0-8476-7932-2 |pages=237–268 |url=http://www.ellerman.org/wp-content/uploads/2012/12/IntellectualTrespassingBook.pdf |chapter-url=https://books.google.com/books?id=NgJqXXk7zAAC&pg=PA237 |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20160305012729/http://www.ellerman.org/wp-content/uploads/2012/12/IntellectualTrespassingBook.pdf |archive-date=2016-03-05 |quote-page=237 |quote=[…] When resistors with resistance a and b are placed in series, their compound resistance is the usual sum (hereafter the series sum) of the resistances a + b. If the resistances are placed in parallel, their compound resistance is the parallel sum of the resistances, which is denoted by the full colon […]}} [https://web.archive.org/web/20150917191423/http://www.ellerman.org/Davids-Stuff/Maths/sp_math.doc] (271 pages)

{{cite book |title=Elektromagnetische Felder und Netzwerke: Anwendungen in Mathcad und PSpice |chapter=Chapter 2.11.4.3: Aufstellen der Differentialgleichung aus der komplexen Darstellung - MATHCAD Anwendung 2.11-6: Benutzerdefinierte Operatoren |chapter-url=https://books.google.com/books?id=wBAjBgAAQBAJ&pg=PA246 |language=de |author-first=Otfried |author-last=Georg |date=2013 |orig-date=1999 |edition=1 |series=Springer-Lehrbuch |publisher=Springer-Verlag |isbn=978-3-642-58420-6 |id={{ISBN|3-642-58420-9}} |doi=10.1007/978-3-642-58420-6 |pages=246–248 |url=https://books.google.com/books?id=wBAjBgAAQBAJ |access-date=2019-08-04}} (728 pages)

{{cite web |title=Introduction to Series-Parallel Duality |author-first=David Patterson |author-last=Ellerman |author-link=David Patterson Ellerman |publisher=University of California at Riverside |date=May 2004 |orig-date=1995-03-21 |citeseerx=10.1.1.90.3666 |url=http://www.ellerman.org/wp-content/uploads/2012/12/Series-Parallel-Duality.CV_.pdf |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20190810011716/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.3666&rep=rep1&type=pdf |archive-date=2019-08-10 |quote=The parallel sum of two positive real numbers x:y = [(1/x) + (1/y)]⁻¹ arises in electrical circuit theory as the resistance resulting from hooking two resistances x and y in parallel. There is a duality between the usual (series) sum and the parallel sum. […]}} [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.3666&rep=rep1&type=pdf] (24 pages)

{{cite web |title=INA 326/INA 327 – Precision, Rail-to-Rail I/O Instrumentation Amplifier |publisher=Burr-Brown / Texas Instruments |date=2018 |id=SBOS222D |orig-date=November 2004, November 2001 |pages=3, 9, 13 |url=http://www.ti.com/lit/ds/sbos222d/sbos222d.pdf |access-date=2019-07-13 |url-status=live |archive-url=https://web.archive.org/web/20190713200507/http://www.ti.com/lit/ds/sbos222d/sbos222d.pdf |archive-date=2019-07-13}}

{{cite book |title=Matrix Partial Orders, Shorted Operators and Applications |author-first1=Sujit Kumar |author-last1=Mitra |author-first2=Pochiraju |author-last2=Bhimasankaram |author-first3=Saroj B. |author-last3=Malik |series=Series in Algebra |volume=10 |edition=illustrated 1st |date=2010 |publisher=World Scientific Publishing Co. Pte. Ltd. |isbn=978-981-283-844-5 |id={{ISBN|981-283-844-9}} |url=https://books.google.com/books?id=jbdpDQAAQBAJ&pg=PR1 |access-date=2019-08-19}} (446 pages)

{{cite book |title=WP 34S Owner's Manual |date=2012-11-30 |orig-date=2008-12-09 |edition=3.1 |author-last1=Dale |author-first1=Paul |author-last2=Bonin |author-first2=Walter |pages=1, 14, 32, 66, 116 |url=https://www.thecalculatorstore.com/WebRoot/StoreES3/Shops/eb9376/4DFF/B1DC/FEDD/A50D/CE9B/D94C/9B1F/0982/Manual_wp_34s_3_1-2.pdf |access-date=2019-07-13 |url-status=live |archive-url=https://web.archive.org/web/20190709150106/https://www.thecalculatorstore.com/WebRoot/StoreES3/Shops/eb9376/4DFF/B1DC/FEDD/A50D/CE9B/D94C/9B1F/0982/Manual_wp_34s_3_1-2.pdf |archive-date=2019-07-09}} [https://sourceforge.net/projects/wp34s/] (211 pages)

{{cite book |title=Grundlagen der Elektrotechnik und Elektronik 1: Gleichstromnetzwerke und ihre Anwendungen |chapter=Chapter 2.3.2: Zusammenschaltungen linearer resistiver Zweipole – Parallelschaltung |language=de |author-first1=Steffen |author-last1=Paul |author-first2=Reinhold |author-last2=Paul |publisher=Springer-Verlag |date=2014-10-24 |volume=1 |edition=5 |isbn=978-3-64253948-0 |id={{ISBN|3-64253948-3}} |page=78 |url=https://books.google.com/books?id=ka4UBQAAQBAJ |chapter-url=https://books.google.com/books?id=ka4UBQAAQBAJ&pg=PA78 |access-date=2019-08-04 |quote-page=78 |quote=[…] Bei abgekürzter Schreibweise achte man sorgfältig auf die Anwendung von Klammern. […] Das Parallelzeichen ∥ der Kurzschreibweise hat die gleiche Bedeutung wie ein Multiplikationszeichen. Deshalb können Klammern entfallen.}} (446 pages)

{{cite web |title=Complex Lock mode for WP-34s |author-first=Nigel |author-last=Dowrick |date=2015-05-03 |orig-date=2015-03-16 |work=HP Museum |url=https://www.hpmuseum.org/forum/thread-3398.html |access-date=2019-08-07 |url-status=live |archive-url=https://web.archive.org/web/20190403160655/http://www.hpmuseum.org/forum/thread-3398.html |archive-date=2019-04-03}}

{{cite book |title=WP 34S Owner's Manual |date=2015 |orig-date=2008-12-09 |edition=3.3 |publisher=CreateSpace Independent Publishing Platform |author-last=Bonin |author-first=Walter |isbn=978-1-5078-9107-0}} [https://sourceforge.net/projects/wp34s/]

{{cite book |title=WP 34S Owner's Manual |date=2016-07-11 |orig-date=2008-12-09 |edition=4 |publisher=CreateSpace Independent Publishing Platform |author-last=Bonin |author-first=Walter |isbn=978-1-53366238-5 |id={{ISBN|1-53366238-X}}}} (410 pages)

{{cite book |title=Numerical and Analytical Methods with MATLAB for Electrical Engineers |author-first1=William |author-last1=Bober |author-first2=Andrew |author-last2=Stevens |chapter=Chapter 7.6. Laplace Transforms Applied to Circuits |series=Applied and Computational Mechanics |edition=1 |publisher=CRC Press |date=2016 |isbn=978-1-46657607-0 |id={{ISBN|1-46657607-3}} |page=224 |url=https://books.google.com/books?id=O2POBQAAQBAJ |chapter-url=https://books.google.com/books?id=O2POBQAAQBAJ&pg=PA224}} (388 pages)

{{cite book |title=Linear Circuit Transfer Functions: An Introduction to Fast Analytical Techniques |chapter=Chapter 1.1.2 The Current Divider |author-last=Basso |author-first=Christophe P. |date=2016 |edition=1 |publisher=John Wiley & Sons Ltd. |isbn=978-1-11923637-5 |lccn=2015047967 |page=12 |location=Chichester, West Sussex, New Jersey, USA |url=https://books.google.com/books?id=gjHYCwAAQBAJ |chapter-url=https://books.google.com/books?id=gjHYCwAAQBAJ&pg=PA12 |access-date=2018-12-28}} (464 pages)

{{cite book |title=EECS 16A Designing Information Devices and Systems I |chapter=Chapter 15.7.2 Parallel Resistors |editor-first1=Gireeja |editor-last1=Ranade |editor-first2=Vladimir |editor-last2=Stojanovic |date=Fall 2018 |type=lecture notes |id=Note 15 |page=12 |publisher=University of California, Berkeley |url=https://inst.eecs.berkeley.edu/~ee16a/fa18/lectures/Note15.pdf |chapter-url=https://inst.eecs.berkeley.edu/~ee16a/fa18/lectures/Note15.pdf#page=12 |access-date=2018-12-28 |url-status=live |archive-url=https://web.archive.org/web/20181227224413/https://inst.eecs.berkeley.edu/~ee16a/fa18/lectures/Note15.pdf |archive-date=2018-12-27 |quote-page=12 |quote=[…] This mathematical relationship comes up often enough that it actually has a name: the "parallel operator", denoted ∥. When we say x∥y, it means $\frac{xy}{x+y}$ . Note that this is a mathematical operator and does not say anything about the actual configuration. In the case of resistors the parallel operator is used for parallel resistors, but for other components (like capacitors) this is not the case. […]}} (16 pages)

{{cite web |title=ECE1250 Cookbook – Nodes, Series, Parallel |editor-first=Neil E. |editor-last=Cotter |date=2015-10-12 |orig-date=2014-09-20 |series=Cookbooks |volume=1 |publisher=University of Utah |type=lecture notes |url=https://utah.instructure.com/files/71709875/download?download_frd=1 |access-date=2019-08-11 |url-status=live |archive-url=https://web.archive.org/web/20200820155936/https://instructure-uploads-2.s3.amazonaws.com/account_20000000000014/attachments/41326888/Cookbook_1NodeSeriesParallel.pdf?response-content-disposition=attachment%3B%20filename%3D%22Cookbook_1NodeSeriesParallel.pdf%22%3B%20filename%2A%3DUTF-8%27%27Cookbook%255F1NodeSeriesParallel.pdf&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJDW777BLV26JM2MQ%2F20200820%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20200820T155936Z&X-Amz-Expires=86400&X-Amz-SignedHeaders=host&X-Amz-Signature=4ebb674156a42fe78d1b31d09fe544c017ddf05b7a0eb9dd5db8370b155e1449 |archive-date=2020-08-20 |quote=[…] One convenient way to indicate two resistors are in parallel is to put a ∥ between them. […]}}

{{cite web |title=Grundlagen der Elektrotechnik Teil B |language=de |author-first=Joachim |author-last=Böcker |date=2019-03-18 |orig-date=April 2008 |publisher=Universität Paderborn |page=12 |url=https://ei.uni-paderborn.de/fileadmin/elektrotechnik/fg/lea/Lehre/GET_B/Dokumente/Skript_GET_B.pdf |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20180417174418/http://ei.uni-paderborn.de/fileadmin/elektrotechnik/fg/lea/Lehre/GET_B/Dokumente/Skript_GET_B.pdf |archive-date=2018-04-17 |quote-page=12 |quote=Für die Berechnung des Ersatzwiderstands der Parallelschaltung wird […] gern die Kurzschreibweise ∥ benutzt.}}

{{cite book |title=WP 43S Owner's Manual |date=2020 |orig-date=2015 |author-last=Bonin |author-first=Walter |isbn=978-1-72950098-9 |id={{ISBN|1-72950098-6}} |edition=draft |version=0.16 |page=119 |url=https://gitlab.com/Over_score/wp43s/-/blob/56341db53bd8cd2dea5b729aa5c41fe8b145182a/draft%20documentation/Owner_wp_43s_0_16s.pdf |access-date=2020-08-20 |url-status=live |archive-url=https://web.archive.org/web/20220721182537if_/https://gitlab.com/Over_score/wp43s/-/raw/56341db53bd8cd2dea5b729aa5c41fe8b145182a/draft%20documentation/Owner_wp_43s_0_16s.pdf?inline=false |archive-date=2022-07-21}} [https://gitlab.com/Over_score/wp43s] [https://sourceforge.net/projects/wp43s/] (328 pages)

{{cite book |title=WP 43S Reference Manual |date=2020 |orig-date=2015 |author-last=Bonin |author-first=Walter |isbn=978-1-72950106-1 |id={{ISBN|1-72950106-0}} |edition=draft |version=0.16 |page=127 |url=https://gitlab.com/Over_score/wp43s/-/blob/56341db53bd8cd2dea5b729aa5c41fe8b145182a/draft%20documentation/Reference_wp_43s_0_16s.pdf |access-date=2020-08-20 |url-status=live |archive-url=https://web.archive.org/web/20220721192805if_/https://gitlab.com/Over_score/wp43s/-/raw/56341db53bd8cd2dea5b729aa5c41fe8b145182a/draft%20documentation/Reference_wp_43s_0_16s.pdf?inline=false |archive-date=2022-07-21}} [https://gitlab.com/Over_score/wp43s] [https://sourceforge.net/projects/wp43s/] (315 pages)

{{cite book |title=TPL5110 Nano-Power System Timer for Power Gating |chapter=7.5.3 Selection of the External Resistance |date=September 2018 |orig-date=January 2015 |id=SNAS650A |version=Revision A |type=Datasheet |publisher=Texas Instruments Incorporated |pages=13–14 |url=https://www.ti.com/lit/ds/symlink/tpl5110.pdf |access-date=2022-09-25 |url-status=live |archive-url=https://web.archive.org/web/20220925151944/https://www.ti.com/lit/ds/symlink/tpl5110.pdf |archive-date=2022-09-25}} (27 pages)

{{cite web |title=A7987: 61 V, 3 A asynchronous step-down switching regulator with adjustable current limitation for automotive |date=2020-09-22 |orig-date=2019-03-19 |id=DS12928 |version=Revision 3 |type=Datasheet |publisher=STMicroelectronics NV |pages=17, 18, 20 |url=https://www.st.com/resource/en/datasheet/a7987.pdf |access-date=2022-07-18 |url-status=live |archive-url=https://web.archive.org/web/20220718205937if_/https://www.st.com/resource/en/datasheet/a7987.pdf |archive-date=2022-07-18}} (36 pages)

}}

External links

https://github.com/microsoftarchive/edx-platform-1/blob/master/common/lib/calc/calc/calc.py

Category:Abstract algebra

Category:Elementary algebra

Category:Multiplication