# Calculating the Log Base 2 of a Number

**QUESTION:** How can I calculate the Log Base 2 of a number or vector in IDL?

** ANSWER:** This answer provided by Martin Leuthi and Med Bennett on the IDL
newsgroup.

The logarithm base N of any number is the natural logarithm of the number
divided by the natural logarithm of the base. For example, here is a program
named **ALOG2** to calculate the base 2 logarithm of a number or vector:

FUNCTION ALOG2, x RETURN, ALOG(x) / ALOG(2) END

Copyright © 1999 David W. Fanning

Last Updated 4 April 1999