mpower

[John W. Eaton]

On 27-Sep-2006, Eric and Diana Luft wrote:

| Is there any Octave equivalent to the matlab "mpower" command, which would 
compute a matrix to an arbitrary, eg fractional, power?  I want to compute a 
matrix to the 2/3 power, but I get a complex-valued matrix as a result, where 
it should be real-valued.  Details follow below, where A2 comes out to be 
complex-valued when I think it should be real-valued:
| 
| M=[1  1  1; 1   2  2; 1  2  3]
| 
| K=[2 -1 .5;-1 1.2 .4;.5 .4 1.8]
| 
| A2=logm(inv(M)*K)^(2/3)

Why do you think it should be real valued?  What are you trying to
compute, the matrix to a fracional power, or the elements to a
fractional power?  When you write the above expression, are you
expecting the matrix (or elements) to be squared first, followed by a
cube-root function?  That is not what you have written.

| Thanks for any help or advice,

Searching for mpower here:

  http://www.mathworks.com/access/helpdesk/help/techdoc/matlab.html

says that mpower is not a Matlab function.  So where did you find
mpower?  Is it part of some external toolbox?  If so, which one?
Where is the documentation for it?

jwe