Factorial Function
Factorial for non-negative integers n <= 170.
fact(n) factorial2(n)
n |
Vector of integers, for |
The factorial is computed by brute force; factorials for n >= 171
are not representable as ‘double’ anymore.
fact returns the factorial of each element in n.
If n < 0 the value is NaN, and for n > 170
it is Inf.
Non-integers will be reduced to integers through floor(n).
factorial2 returns the product of all even resp. odd integers,
depending on whether n is even or odd.
The R core function factorial uses the gamma function,
whose implementation is not accurate enough for larger input values.
fact(c(-1, 0, 1, NA, 171)) #=> NaN 1 1 NA Inf fact(100) #=> 9.332621544394410e+157 factorial(100) #=> 9.332621544394225e+157 # correct value: 9.332621544394415e+157 # Stirling's approximation: 9.324847625269420e+157 # n! ~ sqrt(2*pi*n) * (n/e)^n factorial2(8); factorial2(9); factorial2(10) # 384 945 3840 factorial(10) / factorial2(10) # => factorial2(9)
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