Return a row vector with n elements logarithmically spaced from 10^a to 10^b.
If n is unspecified it defaults to 50.
If b is equal to pi, the points are between 10^a and pi, not 10^a and 10^pi, in order to be compatible with the corresponding MATLAB function.
Also for compatibility with MATLAB, return the second argument b if fewer than two values are requested.
See also: linspace.