Factorial computes the factorial of a number. Given a number n it computes n! (n factorial). You can follow this after launching the R Gui. 5! is same as 5x4x3x2x1

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> factorial(5)

[1] 120

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factorial in R programming is also applicable to non-integers.

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> factorial(5.5)

[1] 287.8853

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How does R programming calculates factorial. It is calculated in the most efficient manner using the Gamma function.

factorial(x)=gamma(x+1)

In implementation to calculate factorial R calculates the gamma

factorial(5)=gamma(5+1)

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> gamma(5+1)

[1] 120 - This is same as factorial(5)

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What about lfactorial in R programming?

The definition of lfactorial (http://www.stata.com/manuals13/m-5factorial.pdf) is ;

lfactorial(n) is log(factorial(n))

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> lfactorial(5)

[1] 4.787492

> log(factorial(5))

[1] 4.787492

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Another interesting tip is you can use factorial function presenting it with a list like factorial(c(5,4,3)) and not a number. It would then compute the factorial for each of the numbers. For example:

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> factorial(c(5,4,3))

[1] 120 24 6

> factorial(c(5,4.3,2))

[1] 120.00000 38.07798 2.00000

> lfactorial(c(5,4,3))

[1] 4.787492 3.178054 1.791759

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---------------

> factorial(5)

[1] 120

---------------

factorial in R programming is also applicable to non-integers.

------

> factorial(5.5)

[1] 287.8853

-------------

How does R programming calculates factorial. It is calculated in the most efficient manner using the Gamma function.

factorial(x)=gamma(x+1)

In implementation to calculate factorial R calculates the gamma

factorial(5)=gamma(5+1)

------

> gamma(5+1)

[1] 120 - This is same as factorial(5)

----

What about lfactorial in R programming?

The definition of lfactorial (http://www.stata.com/manuals13/m-5factorial.pdf) is ;

lfactorial(n) is log(factorial(n))

-----

> lfactorial(5)

[1] 4.787492

> log(factorial(5))

[1] 4.787492

------------

Another interesting tip is you can use factorial function presenting it with a list like factorial(c(5,4,3)) and not a number. It would then compute the factorial for each of the numbers. For example:

----

> factorial(c(5,4,3))

[1] 120 24 6

> factorial(c(5,4.3,2))

[1] 120.00000 38.07798 2.00000

> lfactorial(c(5,4,3))

[1] 4.787492 3.178054 1.791759

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