FACTORIAL
Syntax | Return Value | Arguments | Keywords | Examples | Version History | See Also
The FACTORIAL function computes the factorial N! For integers, the factorial is computed as (N) Þ (N – 1) Þ (N – 2) Þ ... Þ 3 Þ 2 Þ 1. For non-integers the factorial is computed using GAMMA( N+1 ).
This routine is written in the IDL language. Its source code can be found in the file factorial.pro in the lib subdirectory of the IDL distribution.
Syntax
Result = FACTORIAL( N [, /STIRLING] [, /UL64] )
Return Value
Returns the product of the non-negative scalar value or array of values.
Arguments
N
A non-negative scalar or array of values.
Note
Large values of N will cause floating-point overflow errors. The maximum size of N varies with machine architecture. On machines that support the IEEE standard for floating-point arithmetic, the maximum value of N is 170. See MACHAR for a discussion of machine-specific parameters affecting floating-point arithmetic.
Keywords
STIRLING
Set this keyword to use Stirling's asymptotic formula to approximate N!:
where e is the base of the natural logarithm.
UL64
Set this keyword to return the results as unsigned 64-bit integers. This keyword is ignored if STIRLING is set.
Note
Unsigned 64-bit integers will overflow for values of N greater than 20.
Examples
Compute 20!:
IDL prints:
Version History
