Re: mpower

[Joe Koski]

on 9/27/06 8:38 PM, John W. Eaton at address@hidden wrote:

> 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
> 
John, Eric,

I found MATLAB mpower on the webpage

http://www.mathworks.com/access/helpdesk/help/toolbox/simulink/slref/index.h
tml?/access/helpdesk/help/toolbox/simulink/slref/bqthivm-12.html

It says that it is "Equivalent of array power operator (.^)"

Joe