MATLAB: Applying log to matrix converts from real to complex: why

Question

Hello everyone,

I'm experiencing a very strange behaviour from matlab: I have a 132×4 matrix of real numbers and I need to take their logs. Of course, if I take each number's log individually, it works fine. If I instead use the function log on the whole matrix transf = log(matrix); numbers are converted to their logs from row 1 to 64, but from row 65 to the end they are converted to complex numbers (NaNs as well).

What can this be caused by?

Thanks in advance

Answer 1

maybe you have negativ numbers

 log(-1.5)

it's a complex logarithm

http://en.wikipedia.org/wiki/Complex_logarithm