I'd like to solve overdetermined system of linear equations (in fact to fit experimental data)

(like y1=C1*X11+C2*X12+...+Cm1*X1m)

y2=C1*X21+C2*X22+..+Cm*X2m

....

yn=C1*Xn1+C2*Xn2+...Cm*Xnm)

sometimes n>>m sometimes n>~m ,

*yi*and

*xij*are known coefficients

and I know ab initio that all unknowns C1...Cm are positive. Are there specific algorithms developed for such problem? I tried to solve it with simplest least square, but I always get someting like oscillations with increase of

*m*- Positive

*C*are compensated by negative

*C*and fit becomes perfect but it does not have physical sence.

Thanks,

Sergei.