Binomial: Difference between revisions

Latest revision as of 21:50, 10 September 2022

Binomial (!) is a dyadic scalar function which gives the binomial coefficient ${\tbinom {n}{k}}$ between the two arguments. The argument order k!n is reversed compared to most of traditional mathematical notation's alternative notations, for example $C(n,k)$ and $_{n}C_{k}$ , but not others, like $C_{n}^{k}$ . Binomial shares the glyph ! with the monadic arithmetic function Factorial.

Examples

For non-negative integer arguments, the binomial coefficient k!n is equal to the number of ways to choose k items out of n distinct items. For example, 3!5 is 10 because there are 10 ways to pick 3 items out of 5: 123, 124, 125, 134, 135, 145, 234, 235, 245, 345.

      0 1 2 3 4 5!5
1 5 10 10 5 1

k!n also corresponds to the k-th value (zero-indexed) on the n-th row (also zero-indexed) of Pascal's triangle.

      ⍉∘.!⍨ 0,⍳5
1 0  0  0 0 0
1 1  0  0 0 0
1 2  1  0 0 0
1 3  3  1 0 0
1 4  6  4 1 0
1 5 10 10 5 1

Works in: Dyalog APL

Properties

The value of X!Y equals (!Y)÷(!X)×!Y-X.

      Alt←{(!⍵)÷(!⍺)×!⍵-⍺}
      0 1 2 3 4 5 Alt 5
1 5 10 10 5 1

In multiple implementations where Factorial is extended to use the Gamma function $\Gamma (n)$ , Binomial is defined to use the above equality for non-integers. In that case, the Beta function $\mathrm {B} (x,y)$ becomes closely related to the Binomial, giving the identity $\mathrm {B} (X,Y)$ $\Leftrightarrow$ ÷Y×(X-1)!X+Y-1.

      1 1.2 1.4 1.6 1.8 2!5
5 6.105689248 7.219424686 8.281104786 9.227916704 10
      2!3j2
1J5

Works in: Dyalog APL

External links

Documentation

APL built-ins [edit]
Primitives (Timeline)	Functions
Scalar
		Monadic	Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
		Dyadic	Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
Non-Scalar
		Structural	Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
		Selection	First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
		Selector	Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
		Computational	Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Operators	Monadic	Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
Operators	Dyadic	Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
Quad names	Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector

@@ Line 1: / Line 1: @@
-{{Built-in|Binomial|!}} is a [[dyadic]] [[scalar function]] which gives the [[wikipedia:binomial coefficient|binomial coefficient]] <math>\tbinom nk</math> between the two [[argument|arguments]]. The argument order <syntaxhighlight lang=apl inline>k!n</source> is reversed compared to most of traditional mathematical notation's alternative notations, for example <math>C(n,k)</math> and <math>_nC_k</math>, but not others, like <math>C_n^k</math>. Binomial shares the [[glyph]] <syntaxhighlight lang=apl inline>!</source> with the monadic arithmetic function [[Factorial]].
+{{Built-in|Binomial|!}} is a [[dyadic]] [[scalar function]] which gives the [[wikipedia:binomial coefficient|binomial coefficient]] <math>\tbinom nk</math> between the two [[argument|arguments]]. The argument order <syntaxhighlight lang=apl inline>k!n</syntaxhighlight> is reversed compared to most of traditional mathematical notation's alternative notations, for example <math>C(n,k)</math> and <math>_nC_k</math>, but not others, like <math>C_n^k</math>. Binomial shares the [[glyph]] <syntaxhighlight lang=apl inline>!</syntaxhighlight> with the monadic arithmetic function [[Factorial]].
 == Examples ==
-For non-negative integer arguments, the binomial coefficient <syntaxhighlight lang=apl inline>k!n</source> is equal to the number of ways to choose k items out of n distinct items. For example, <syntaxhighlight lang=apl inline>3!5</source> is 10 because there are 10 ways to pick 3 items out of 5: 123, 124, 125, 134, 135, 145, 234, 235, 245, 345.
+For non-negative integer arguments, the binomial coefficient <syntaxhighlight lang=apl inline>k!n</syntaxhighlight> is equal to the number of ways to choose k items out of n distinct items. For example, <syntaxhighlight lang=apl inline>3!5</syntaxhighlight> is 10 because there are 10 ways to pick 3 items out of 5: 123, 124, 125, 134, 135, 145, 234, 235, 245, 345.
 <syntaxhighlight lang=apl>
 1 2 3 4 5!5
 5 10 10 5 1
-</source>
+</syntaxhighlight>
-<syntaxhighlight lang=apl inline>k!n</source> also corresponds to the k-th value (zero-indexed) on the n-th row (also zero-indexed) of [[wikipedia:Pascal's triangle|Pascal's triangle]].
+<syntaxhighlight lang=apl inline>k!n</syntaxhighlight> also corresponds to the k-th value (zero-indexed) on the n-th row (also zero-indexed) of [[wikipedia:Pascal's triangle|Pascal's triangle]].
 <syntaxhighlight lang=apl>
@@ Line 20: / Line 20: @@
 4  6  4 1 0
 5 10 10 5 1
-</source>{{Works in|[[Dyalog APL]]}}
+</syntaxhighlight>{{Works in|[[Dyalog APL]]}}
 == Properties ==
-The value of <syntaxhighlight lang=apl inline>X!Y</source> equals <syntaxhighlight lang=apl inline>(!Y)÷(!X)×!Y-X</source>.
+The value of <syntaxhighlight lang=apl inline>X!Y</syntaxhighlight> equals <syntaxhighlight lang=apl inline>(!Y)÷(!X)×!Y-X</syntaxhighlight>.
 <syntaxhighlight lang=apl>
@@ Line 30: / Line 30: @@
 1 2 3 4 5 Alt 5
 5 10 10 5 1
-</source>
+</syntaxhighlight>
-In multiple implementations where [[Factorial]] is extended to use the [[wikipedia:Gamma function|Gamma function]] <math>\Gamma(n)</math>, Binomial is defined to use the above equality for non-integers. In that case, the [[wikipedia:Beta function|Beta function]] <math>\Beta(x,y)</math> becomes closely related to the Binomial, giving the identity <math>\Beta(X,Y)</math>{{←→}}<syntaxhighlight lang=apl inline>÷Y×(X-1)!X+Y-1</source>.
+In multiple implementations where [[Factorial]] is extended to use the [[wikipedia:Gamma function|Gamma function]] <math>\Gamma(n)</math>, Binomial is defined to use the above equality for non-integers. In that case, the [[wikipedia:Beta function|Beta function]] <math>\Beta(x,y)</math> becomes closely related to the Binomial, giving the identity <math>\Beta(X,Y)</math>{{←→}}<syntaxhighlight lang=apl inline>÷Y×(X-1)!X+Y-1</syntaxhighlight>.
 <syntaxhighlight lang=apl>
@@ Line 39: / Line 39: @@
 !3j2
 J5
-</source>{{Works in|[[Dyalog APL]]}}
+</syntaxhighlight>{{Works in|[[Dyalog APL]]}}
 == External links ==

Binomial: Difference between revisions

Latest revision as of 21:50, 10 September 2022

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Examples

Properties

External links

Documentation

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Binomial: Difference between revisions

Latest revision as of 21:50, 10 September 2022

Examples

Properties

External links

Documentation

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