TreeTools (version 1.4.1)

DoubleFactorial: Double factorial

Description

Calculate the double factorial of a number, or its logarithm.

Usage

DoubleFactorial(n)

DoubleFactorial64(n)

LnDoubleFactorial(n)

Log2DoubleFactorial(n)

LogDoubleFactorial(n)

LnDoubleFactorial.int(n)

LogDoubleFactorial.int(n)

Arguments

n

Vector of integers.

Value

Returns the double factorial, n * (n - 2) * (n - 4) * (n - 6) * ...

Functions

  • DoubleFactorial64: Returns the exact double factorial as a 64-bit integer64, for n < 34.

  • LnDoubleFactorial: Returns the logarithm of the double factorial.

  • Log2DoubleFactorial: Returns the logarithm of the double factorial.

  • LnDoubleFactorial.int: Slightly faster, when x is known to be length one and below 50001

See Also

Other double factorials: doubleFactorials, logDoubleFactorials

Examples

Run this code
# NOT RUN {
DoubleFactorial (-4:0) # Return 1 if n < 2
DoubleFactorial (2) # 2
DoubleFactorial (5) # 1 * 3 * 5
exp(LnDoubleFactorial.int (8)) # log(2 * 4 * 6 * 8)
DoubleFactorial64(31)
# }

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