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<!--Many mathematics curricula developed according to the 1989 standards of the [[NCTM]] do not teach standard arithmetic methods, instead guiding students to invent their own methods of computation. Though widely adopted by many school districts in nations such as the United States, they have encountered resistance from some parents and mathematicians, and some districts have since abandoned such curricula in favor of [[traditional mathematics]].--><!-- linked from below --><!-- This section (letter)]] and [[Capital Pi notation]] --><!-- linked from below --><!-- linked from above -->
{{Redirect|Multiply|other uses|Multiplication (disambiguation)}}
{{Redirect|Times|the typeface|Times (typeface)|the UK newspaper|The Times|other uses|The Times (disambiguation)}}
{{For|methods of computing products, including those of very large numbers|Multiplication algorithm}}
{{refimprove|date=April 2012}}

[[File:Multiply 4 bags 3 marbles.svg|thumb|right|Four bags of three [[Marble (toy)|marbles]] gives twelve marbles (4 × 3 = 12).]]

[[File:Multiplication as scaling integers.gif|thumb|right|Multiplication can also be thought of as scaling. In the above animation, we see 2 being multiplied by 3, giving 6 as a result]]

[[File:Multiplication scheme 4 by 5.jpg|thumb|right|4 × 5 = 20, the rectangle is composed of 20 squares, having dimensions of 4 by 5.]]

[[File:Multiply field fract.svg|thumb|right|Area of a cloth 4.5m&nbsp;×&nbsp;2.5m&nbsp;= 11.25m<sup>2</sup>; 4½&nbsp;×&nbsp;2½ =&nbsp;11¼]]

'''Multiplication''' (often denoted by the cross symbol "'''[[×]]'''") is the [[Operation (mathematics)|mathematical operation]] of scaling one number by another. It is one of the four basic operations in [[elementary arithmetic]] (the others being [[addition]], [[subtraction]] and [[division (mathematics)|division]]).

Because the result of scaling by [[Natural number|whole numbers]] can be thought of as consisting of some number of copies of the original, whole-number products greater than 1 can be computed by repeated addition; for example, 3 multiplied by 4 (often said as "3 times 4") can be calculated by adding 4 copies of 3 together:

:<math>3 \times 4 = 3 + 3 + 3 + 3 = 12.\!\,</math>

Here 3 and 4 are the "factors" and 12 is the "product".

Educators differ as to which number should normally be considered as the number of copies, and whether multiplication should even be introduced as repeated addition.<ref>{{cite web|url=http://www.globaledresources.com/resources/assets/042309_Multiplication_v2.pdf | title=Is Multiplication Just Repeated Addition?|author=Makoto Yoshida| year=2009 }}</ref> For example 3 multiplied by 4 can also be calculated by adding 3 copies of 4 together:

:<math>3 \times 4 = 4 + 4 + 4 = 12.\!\,</math>

Multiplication of [[rational number]]s (fractions) and [[real number]]s is defined by systematic [[Multiplication#Multiplication of different kinds of numbers|generalization]] of this basic idea.

Multiplication can also be visualized as counting objects arranged in a [[rectangle]] (for whole numbers) or as finding the [[area]] of a rectangle whose sides have given [[length]]s (for numbers generally). The area of a rectangle does not depend on which side you measure first, which illustrates that the order numbers are multiplied together in doesn't matter.

In general the result of multiplying two measurements gives a result of a new type depending on the measurements. For instance:

:<math>2.5 \mbox{ meters} \times 4.5 \mbox{ meters} = 11.25 \mbox{ square meters},\!\,</math>
:<math>11 \mbox{ meters/second} \times 9 \mbox{ seconds} = 99 \mbox{ meters}.\!\,</math>

The inverse operation of multiplication is division. For example, 4 multiplied by 3 equals 12. Then 12 divided by 3 equals 4. Multiplication by 3, followed by division by 3, yields the original number.

Multiplication is also defined for other types of numbers (such as [[complex number]]s), and for more abstract constructs such as [[matrix (mathematics)|matrices]]. For these more abstract constructs, the order that the operands are multiplied in sometimes does matter.

==Notation and terminology==
{{Unreferenced section|date=August 2011}}
{{Calculation results}}
[[Image:Multiplication Sign.svg|thumb|right|The multiplication sign &times;<br/> ([[Character encodings in HTML|HTML entity]] is <tt>&amp;times;</tt>)]]

Multiplication is often written using the [[multiplication sign]] "×" between the terms; that is, in [[infix notation]]. The result is expressed with an [[equals sign]]. For example,

:<math>2\times 3 = 6</math> (verbally, "two times three equals six")

:<math>3\times 4 = 12</math>

:<math>2\times 3\times 5 = 6\times 5 = 30</math>

:<math>2\times 2\times 2\times 2\times 2 = 32</math>

There are several other common notations for multiplication. Many of these are intended to reduce confusion between the multiplication sign × and the commonly used variable x:

*Multiplication is sometimes denoted by either a [[middle dot]] or a [[Full stop|period]]:

:<math>5 \cdot 2 \quad\text{or}\quad 5\,.\,2</math>

:The middle dot is standard in the [[United States]], the [[United Kingdom]], and other countries where the period is used as a [[decimal separator|decimal point]]. In other countries that use a [[Comma (punctuation)|comma]] as a decimal point, either the period or a middle dot is used for multiplication.{{citation needed|date=August 2011}} Internationally, the middle dot is commonly connotated with a more advanced or scientific use.{{citation needed|date=March 2013}}

*The [[asterisk]] (as in <code>5*2</code>) is often used in [[programming language]]s because it appears on every keyboard. This usage originated in the [[FORTRAN]] programming language.

*In [[algebra]], multiplication involving [[Variable (mathematics)|variables]] is often written as a [[wikt:juxtaposition|juxtaposition]] (e.g., ''xy'' for ''x'' times ''y'' or 5''x'' for five times ''x''). This notation can also be used for quantities that are surrounded by [[Bracket#Parentheses %28 %29|parentheses]] (e.g., 5(2) or (5)(2) for five times two).

*In [[matrix multiplication]], there is actually a distinction between the cross and the dot symbols. The cross symbol generally denotes a vector multiplication, while the dot denotes a scalar multiplication. A similar convention distinguishes between the [[cross product]] and the [[dot product]] of two [[vector (mathematics)|vectors]].

The numbers to be multiplied are generally called the "[[factorization|factors]]" or "multiplicands". When thinking of multiplication as repeated addition, the number to be multiplied is called the "multiplicand", while the number of multiples is called the "multiplier". In algebra, a number that is the multiplier of a variable or expression (e.g., the 3 in 3''xy''<sup>2</sup>) is called a [[coefficient]].

The result of a multiplication is called a [[product (mathematics)|product]], and is a [[multiple (mathematics)|multiple]] of each factor if the other factor is an integer. For example, 15 is the product of 3 and 5, and is both a multiple of 3 and a multiple of 5.

==Computation==

The common methods for multiplying numbers using pencil and paper require a [[multiplication table]] of memorized or consulted products of small numbers (typically any two numbers from 0 to 9), however one method, the [[Ancient Egyptian multiplication|peasant multiplication]] algorithm, does not. <!--Many mathematics curricula developed according to the 1989 standards of the [[NCTM]] do not teach standard arithmetic methods, instead guiding students to invent their own methods of computation. Though widely adopted by many school districts in nations such as the United States, they have encountered resistance from some parents and mathematicians, and some districts have since abandoned such curricula in favor of [[traditional mathematics]].-->

Multiplying numbers to more than a couple of decimal places by hand is tedious and error prone. [[Common logarithm]]s were invented to simplify such calculations. The [[slide rule]] allowed numbers to be quickly multiplied to about three places of accuracy. Beginning in the early twentieth century, mechanical [[calculator]]s, such as the [[Marchant Calculator|Marchant]], automated multiplication of up to 10 digit numbers. Modern electronic [[computer]]s and calculators have greatly reduced the need for multiplication by hand.

===Historical algorithms===
Methods of multiplication were documented in the [[Ancient Egypt|Egyptian]], [[Ancient Greece|Greek]], [[Ancient India|Indian]] and [[History of China#Ancient China|Chinese]] civilizations.

The [[Ishango bone]], dated to about 18,000 to 20,000 BC, hints at a knowledge of multiplication in the [[Upper Paleolithic]] era in [[Central Africa]].

====Egyptians====
{{Main|Ancient Egyptian multiplication}}
The Egyptian method of multiplication of integers and fractions, documented in the [[Ahmes Papyrus]], was by successive additions and doubling. For instance, to find the product of 13 and 21 one had to double 21 three times, obtaining 1 × 21 = 21, 2 × 21 = 42, 4 × 21 = 84, 8 × 21 = 168. The full product could then be found by adding the appropriate terms found in the doubling sequence:
:13 × 21 = (1 + 4 + 8) × 21 = (1 × 21) + (4 × 21) + (8 × 21) = 21 + 84 + 168 = 273.

====Babylonians====
The [[Babylonians]] used a [[sexagesimal]] [[positional number system]], analogous to the modern day [[decimal expansion|decimal system]]. Thus, Babylonian multiplication was very similar to modern decimal multiplication. Because of the relative difficulty of remembering 60 × 60 different products, Babylonian mathematicians employed [[multiplication table]]s. These tables consisted of a list of the first twenty multiples of a certain ''principal number'' ''n'': ''n'', 2''n'', ..., 20''n''; followed by the multiples of 10''n'': 30''n'' 40''n'', and 50''n''. Then to compute any sexagesimal product, say 53''n'', one only needed to add 50''n'' and 3''n'' computed from the table.

====Chinese====
[[File:Multiplication algorithm.GIF|thumb|right|250px|38&nbsp;'''×'''&nbsp;76&nbsp;=&nbsp;2888]]
In the mathematical text ''[[Zhou Bi Suan Jing]]'', dated prior to 300 BC, and the ''[[Nine Chapters on the Mathematical Art]]'', multiplication calculations were written out in words, although the early Chinese mathematicians employed [[Rod calculus]] involving place value addition, subtraction, multiplication and division. These place value decimal arithmetic algorithms were introduced by [[Al Khwarizmi]] to Arab countries in the early 9th century.

===Modern method===
[[Image:Gelosia multiplication 45 256.png|right|250px|thumb|Product of 45 and 256. Note the order of the numerals in 45 is reversed down the left column. The carry step of the multiplication can be performed at the final stage of the calculation (in bold), returning the final product of 45&nbsp;'''×'''&nbsp;256&nbsp;=&nbsp;11520.]]
The modern method of multiplication based on the [[Hindu–Arabic numeral system]] was first described by [[Brahmagupta]]. Brahmagupta gave rules for addition, subtraction, multiplication and division. [[Henry Burchard Fine]], then professor of Mathematics at [[Princeton University]], wrote the following:
:''The Indians are the inventors not only of the positional decimal system itself, but of most of the processes involved in elementary reckoning with the system. Addition and subtraction they performed quite as they are performed nowadays; multiplication they effected in many ways, ours among them, but division they did cumbrously.''<ref>Henry B. Fine. ''The Number System of Algebra – Treated Theoretically and Historically'', (2nd edition, with corrections, 1907), page 90, http://www.archive.org/download/numbersystemofal00fineuoft/numbersystemofal00fineuoft.pdf</ref>

===Computer algorithms===
{{Main|Multiplication algorithm}}

The standard method of multiplying two ''n''-digit numbers requires ''n''<sup>2</sup> simple multiplications. [[Multiplication algorithm]]s have been designed that reduce the computation time considerably when multiplying large numbers. In particular for very large numbers methods based on the [[Discrete_Fourier_transform#Multiplication_of_large_integers|Discrete Fourier Transform]] can reduce the number of simple multiplications to the order of ''n'' log<sub>2</sub>(''n'').

==Products of measurements==
{{Main|Dimensional analysis}}

When two measurements are multiplied together the product is of a type depending on the types of the measurements. The general theory is given by [[dimensional analysis]]. This analysis is routinely applied in physics but has also found applications in finance. One can only meaningfully add or subtract quantities of the same type but can multiply or divide quantities of different types.

A common example is multiplying speed by time gives distance, so

:50 kilometers per hour × 3 hours = 150 kilometers.

==Products of sequences==<!-- linked from below -->
===Capital Pi notation===<!-- This section (letter)]] and [[Capital Pi notation]] -->

The product of a sequence of terms can be written with the product symbol, which derives from the capital letter Π (Pi) in the [[Greek alphabet]]. Unicode position U+220F (∏) contains a glyph for denoting such a product, distinct from U+03A0 (Π), the letter. The meaning of this notation is given by:

: <math> \prod_{i=m}^n x_i = x_m \cdot x_{m+1} \cdot x_{m+2} \cdot \,\,\cdots\,\, \cdot x_{n-1} \cdot x_n. </math>

The subscript gives the symbol for a [[free variables and bound variables|dummy variable]] (''i'' in this case), called the "index of multiplication" together with its lower bound (''m''), whereas the superscript (here ''n'') gives its upper bound. The lower and upper bound are expressions denoting integers. The factors of the product are obtained by taking the expression following the product operator, with successive integer values substituted for the index of multiplication, starting from the lower bound and incremented by 1 up to and including the upper bound. So, for example:

: <math> \prod_{i=2}^6 \left(1 + {1\over i}\right) = \left(1 + {1\over 2}\right) \cdot \left(1 + {1\over 3}\right) \cdot \left(1 + {1\over 4}\right) \cdot \left(1 + {1\over 5}\right) \cdot \left(1 + {1\over 6}\right) = {7\over 2}. </math>

In case ''m'' = ''n'', the value of the product is the same as that of the single factor ''x''<sub>''m''</sub>. If ''m''&nbsp;>&nbsp;''n'', the product is the [[empty product]], with the value&nbsp;1.

===Infinite products===
{{Main|Infinite product}}

One may also consider products of infinitely many terms; these are called [[infinite product]]s. Notationally, we would replace ''n'' above by the [[lemniscate]] ∞. The product of such a series is defined as the [[limit of a sequence|limit]] of the product of the first ''n'' terms, as ''n'' grows without bound. That is, by definition,

: <math> \prod_{i=m}^{\infty} x_{i} = \lim_{n\to\infty} \prod_{i=m}^{n} x_{i}. </math>

One can similarly replace ''m'' with negative infinity, and define:

:<math>\prod_{i=-\infty}^\infty x_i = \left(\lim_{m\to-\infty}\prod_{i=m}^0 x_i\right) \cdot \left(\lim_{n\to\infty}\prod_{i=1}^n x_i\right),</math>

provided both limits exist.

==Properties==
[[Image:Multiplication chart.png|thumb|Multiplication of numbers 0-10. Line labels = multiplicand. X axis = multiplier. Y axis = product.]]

For the [[real number|real]] and [[complex number|complex]] numbers, which includes for example [[natural number]]s, [[integer]]s and [[rational number|fractions]], multiplication has certain properties:

;'''[[commutative|Commutative property]]'''
: The order in which two numbers are multiplied does not matter:
::<math>x\cdot y = y\cdot x</math>.

;'''[[associative|Associative property]]'''
: Expressions solely involving multiplication or addition are invariant with respect to [[order of operations]]:
::<math>(x\cdot y)\cdot z = x\cdot(y\cdot z)</math>

;'''[[distributive|Distributive property]]'''
: Holds with respect to multiplication over addition. This identity is of prime importance in simplifying algebraic expressions:
::<math>x\cdot(y + z) = x\cdot y + x\cdot z </math>

;'''[[Identity element]]'''
: The multiplicative identity is 1; anything multiplied by one is itself. This is known as the identity property:
::<math>x\cdot 1 = x</math>

;'''[[Absorbing element|Zero element]]'''
: Any number multiplied by zero is zero. This is known as the zero property of multiplication:
::<math>x\cdot 0 = 0</math>
:Zero is sometimes not included amongst the natural numbers.

There are a number of further properties of multiplication not satisfied by all types of numbers.

;Negation
:Negative one times any number is equal to the opposite of that number.
::<math>(-1)\cdot x = (-x)</math>

: Negative one times negative one is positive one.
::<math>(-1)\cdot (-1) = 1</math>

:The natural numbers do not include negative numbers.

;'''[[Inverse element]]'''
:Every number ''x'', except zero, has a '''[[multiplicative inverse]]''', <math>\frac{1}{x}</math>, such that <math>x\cdot\left(\frac{1}{x}\right) = 1</math>.

;Order preservation
: Multiplication by a positive number preserves [[Order theory|order]]: if ''a''&nbsp;>&nbsp;0, then if ''b''&nbsp;>&nbsp;''c'' then ''ab''&nbsp;>&nbsp;''ac''. Multiplication by a negative number '''reverses''' order: if ''a''&nbsp;<&nbsp;0 and ''b''&nbsp;>&nbsp;''c'' then ''ab''&nbsp;<&nbsp;''ac''.
:The complex numbers do not have an order predicate.

Other mathematical systems that include a multiplication operation may not have all these properties. For example, multiplication is not, in general, commutative for matrices and [[quaternion]]s.

==Axioms==
{{Main|Peano axioms}}

In the book ''Arithmetices principia, nova methodo exposita'', [[Giuseppe Peano]] proposed axioms for arithmetic based on his axioms for natural numbers.<ref>[http://planetmath.org/encyclopedia/PeanoArithmetic.html PlanetMath: Peano arithmetic<!-- Bot generated title -->]</ref> Peano arithmetic has two axioms for multiplication:

:<math>x \times 0 = 0</math>
:<math>x \times S(y) = (x \times y) + x</math>

Here ''S''(''y'') represents the [[Successor ordinal|successor]] of ''y'', or the natural number that ''follows'' ''y''. The various properties like associativity can be proved from these and the other axioms of Peano arithmetic including [[Mathematical induction|induction]]. For instance ''S''(0). denoted by 1, is a multiplicative identity because

:<math>x \times 1 = x \times S(0) = (x \times 0) + x = 0 + x = x </math>

The axioms for [[integer]]s typically define them as equivalence classes of ordered pairs of natural numbers. The model is based on treating (''x'',''y'') as equivalent to ''x''−''y'' when ''x'' and ''y'' are treated as integers. Thus both (0,1) and (1,2) are equivalent to −1. The multiplication axiom for integers defined this way is

:<math>(x_p,\, x_m) \times (y_p,\, y_m) = (x_p \times y_p + x_m \times y_m,\; x_p \times y_m + x_m \times y_p)</math>

The rule that −1 × −1 = 1 can then be deduced from

:<math>(0, 1) \times (0, 1) = (0 \times 0 + 1 \times 1,\, 0 \times 1 + 1 \times 0) = (1,0)</math>

Multiplication is extended in a similar way to [[rational number]]s and then to [[real number]]s.

==Multiplication with set theory==

It is possible, though difficult, to create a recursive definition of multiplication with set theory. Such a system usually relies on the [[Peano_axioms#Arithmetic|Peano definition of multiplication]].

===Cartesian product===
The definition of multiplication as repeated [[addition]] provides a way to arrive at a set-theoretic interpretation of multiplication of [[cardinal numbers]]. In the expression

: <math>\displaystyle n \cdot a = \underbrace{a + \cdots + a}_{n},</math>

if the ''n'' copies of ''a'' are to be combined in disjoint union then clearly they must be made disjoint; an obvious way to do this is to use either ''a'' or ''n'' as the indexing set for the other. Then, the members of <math>n \cdot a\,</math> are exactly those of the [[Cartesian product]] <math>n \times a\,</math>. The properties of the multiplicative operation as applying to natural numbers then follow trivially from the corresponding properties of the Cartesian product.

==Multiplication in group theory==<!-- linked from below -->
There are many sets that, under the operation of multiplication, satisfy the axioms that define [[group (mathematics)|group]] structure. These axioms are closure, associativity, and the inclusion of an identity element and inverses.

A simple example is the set of non-zero [[rational numbers]]. Here we have identity 1, as opposed to groups under addition where the identity is typically 0. Note that with the rationals, we must exclude zero because, under multiplication, it does not have an inverse: there is no rational number that can be multiplied by zero to result in 1. In this example we have an [[abelian group]], but that is not always the case.

To see this, look at the set of invertible square matrices of a given dimension, over a given [[field (mathematics)|field]]. Now it is straightforward to verify closure, associativity, and inclusion of identity (the [[identity matrix]]) and inverses. However, matrix multiplication is not commutative, therefore this group is nonabelian.

Another fact of note is that the integers under multiplication is not a group, even if we exclude zero. This is easily seen by the nonexistence of an inverse for all elements other than 1 and -1.

Multiplication in group theory is typically notated either by a dot, or by juxtaposition (the omission of an operation symbol between elements). So multiplying element '''a''' by element '''b''' could be notated '''a''' <math>\cdot</math> '''b''' or '''ab'''. When referring to a group via the indication of the set and operation, the dot is used, e.g., our first example could be indicated by <math>\left( \mathbb{Q}\smallsetminus \{ 0 \} ,\cdot \right) </math>

== Multiplication of different kinds of numbers ==<!-- linked from above -->

Numbers can ''count'' (3 apples), ''order'' (the 3rd apple), or ''measure'' (3.5 feet high); as the history of mathematics has progressed from counting on our fingers to modelling quantum mechanics, multiplication has been generalized to more complicated and abstract types of numbers, and to things that are not numbers (such as [[Matrix (mathematics)|matrices]]) or do not look much like numbers (such as [[quaternion]]s).

;'''Integers'''
:<math>N\times M</math> is the sum of ''M'' copies of ''N'' when ''N'' and ''M'' are positive whole numbers. This gives the number of things in an array ''N'' wide and ''M'' high. Generalization to negative numbers can be done by <math>N\times (-M) = (-N)\times M = - (N\times M)</math> and <math>(-N)\times (-M) = N\times M</math>. The same sign rules apply to rational and real numbers.

;'''[[Rational number]]s'''
:Generalization to fractions <math>\frac{A}{B}\times \frac{C}{D}</math> is by multiplying the numerators and denominators respectively: <math>\frac{A}{B}\times \frac{C}{D} = \frac{(A\times C)}{(B\times D)}</math>. This gives the area of a rectangle <math>\frac{A}{B}</math> high and <math>\frac{C}{D}</math> wide, and is the same as the number of things in an array when the rational numbers happen to be whole numbers.

;'''[[Real number]]s'''
:<math>(x)(y)</math> is the limit of the products of the corresponding terms in certain sequences of rationals that converge to ''x'' and ''y'', respectively, and is significant in [[calculus]]. This gives the area of a rectangle ''x'' high and ''y'' wide. See [[Multiplication#Products of sequences|Products of sequences]], above.

;'''[[Complex number]]s'''
:Considering complex numbers <math>z_1</math> and <math>z_2</math> as ordered pairs of real numbers <math>(a_1, b_1)</math> and <math>(a_2, b_2)</math>, the product <math>z_1\times z_2</math> is <math>(a_1\times a_2 - b_1\times b_2, a_1\times b_2 + a_2\times b_1)</math>. This is the same as for reals, <math>a_1\times a_2</math>, when the ''imaginary parts'' <math>b_1</math> and <math>b_2</math> are zero.

;'''Further generalizations'''
:See [[Multiplication#Multiplication in group theory|Multiplication in group theory]], above, and [[Multiplicative group|Multiplicative Group]], which for example includes matrix multiplication. A very general, and abstract, concept of multiplication is as the "multiplicatively denoted" (second) binary operation in a [[Ring (mathematics)|ring]]. An example of a ring that is not any of the above number systems is a [[polynomial ring]] (you can add and multiply polynomials, but polynomials are not numbers in any usual sense.)

;'''Division'''
:Often division, <math>\frac{x}{y}</math>, is the same as multiplication by an inverse, <math>x\left(\frac{1}{y}\right)</math>. Multiplication for some types of "numbers" may have corresponding division, without inverses; in an [[integral domain]] ''x'' may have no inverse "<math>\frac{1}{x}</math>" but <math>\frac{x}{y}</math> may be defined. In a [[division ring]] there are inverses but they are not commutative (since <math>\left(\frac{1}{x}\right)\left(\frac{1}{y}\right)</math> is not the same as <math>\left(\frac{1}{y}\right)\left(\frac{1}{x}\right)</math>, <math>\frac{x}{y}</math> may be ambiguous).

==Exponentiation==
{{Main|Exponentiation}}
When multiplication is repeated, the resulting operation is known as '''exponentiation'''. For instance, the product of three factors of two (2×2×2) is "two raised to the third power", and is denoted by 2<sup>3</sup>, a two with a [[superscript]] three. In this example, the number two is the '''base''', and three is the '''exponent'''. In general, the exponent (or superscript) indicates how many times to multiply base by itself, so that the expression

:<math>a^n = \underbrace{a\times a \times \cdots \times a}_n</math>

indicates that the base ''a'' to be multiplied by itself ''n'' times.

==See also==
{{col-begin}}
{{col-break|width=33%}}
* [[Dimensional analysis]]
* [[Multiplication algorithm]]
** [[Karatsuba algorithm]], for large numbers
** [[Toom–Cook multiplication]], for very large numbers
** [[Schönhage–Strassen algorithm]], for huge numbers
{{col-break|width=33%}}
* [[Multiplication table]]
* [[Multiplication ALU]], how computers multiply
** [[Booth's multiplication algorithm]]
** [[Floating point]]
** [[Fused multiply–add]]
** [[Multiply–accumulate]]
** [[Wallace tree]]
{{col-break}}
* [[Multiplicative inverse]], reciprocal
* [[Factorial]]
* [[Genaille–Lucas rulers]]
* [[Napier's bones]]
* [[Peasant multiplication]]
* [[Product (mathematics)]], for generalizations
* [[Slide rule]]
{{col-end}}

==Notes==
{{Reflist}}

==References==
* {{cite book|author = [[Carl Boyer|Boyer, Carl B.]] (revised by Merzbach, Uta C.)|title = History of Mathematics|publisher = John Wiley and Sons, Inc.|year = 1991|isbn = 0-471-54397-7}}

== External links ==
* [http://www.cut-the-knot.org/do_you_know/multiplication.shtml Multiplication] and [http://www.cut-the-knot.org/blue/SysTable.shtml Arithmetic Operations In Various Number Systems] at [[cut-the-knot]]
* [http://webhome.idirect.com/~totton/suanpan/mod_mult/ Modern Chinese Multiplication Techniques on an Abacus]

{{Elementary arithmetic}}


[[Category:Elementary arithmetic]]
[[Category:Elementary arithmetic]]

Revision as of 20:13, 12 August 2013

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