21

In the Programming mode of gcalctool, you have a log button, which calculates the logarithm, but how do I know what base it's using and how do I change it?

For example, how would I calculate the base 2 logarithm for 16?

3 Answers 3

27

By default the log button calculates base-10 logarithms (while the "ln" button does, of course, base-e logarithms).

To specify a different base, you use a "subscript":

  • Type "log" in the input field.
  • Input your desired base with a subscript. This can be done either by clicking on the "downarrow-n" button (top left) and then entering the number, or by pressing Alt while typing the number.
  • Finally type the number whose logarithm you want to calculate.

By the way, I found this pretty easily by accessing gcalctool's help (press F1) and looking for logarithms in the index.

1
  • 1
    To use a decimal base (e.g. 1.01), use the answer from user247983. E.g. to determine the monthly interest from an APR of 12%, I used ln 1.12 / ln 1.01. If I use the method from this answer (log₁.₀₁ 1.12), it says "Malformed expression". Apr 14, 2015 at 1:07
4

You can also use the base change formula:

ln(1024)/ln(2) = log (base 2) (1024)
0

You may use this frequently and like a button instead of writing out the base change formula again and again. Add within gcalculator (kde) by selecting:

edit preferences functions Name: log2 Variable: x Expression: log(x)/log(2) add update close view buttons functions

now to get log2(1024): type 1024 into the calculator and PRESS ENTER hit the 'fun' button select log2 the answer is 10

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .