Geometric standard deviation

Calculates the geometric standard deviation of an array.

The stats toolbox provides a function to calculate the geometric mean of an array, but a function for the geometric standard deviation is oddly missing.

Here is a function to fill that void, with no toolbox required.

The function accepts a vector, matrix or N-D array; an optional flag to normalise by N or (N-1); and an optional dimension to calculate the gsd across.