[R] Matrix regression

[Corrado]

Dear friends,

I would like to solve the following regression problem:

y=c1 x1 + c2 x2 + .... + cn xn

where the y, xi are all matrices and the ci are constants that need to be 
determined. The y, xi are distance matrices (symmetric). ci should be forced 
to positive or null (i.e. non negative).

Any suggestion? 

I will be more than happy to share the results of my quest with the list or 
developers.

Regards
-- 
Corrado Topi

Global Climate Change & Biodiversity Indicators
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk