[Vxl-users] vnl_sqrt doesnt solve Ax=b

[<do...@vi...>]

vnl_sqrt doesnt solve Ax=b for systems aleardy around 30.

For 20 it gives good results (for a naive linear problem) and:

vnl_lsqr.cxx : x = 0  is the exact solution. No iterations were performed.
vnl_lsqr.cxx : The iteration limit ITNLIM was reached.
vnl_lsqr.cxx : residual norm estimate = 8.40484e-06
vnl_lsqr.cxx : result norm estimate   = 14.6304
vnl_lsqr.cxx : condition no. estimate = 67.683
vnl_lsqr.cxx : iterations             = 20



whereas for 30 equations it goes banana (wrong solution):



vnl_lsqr.cxx : x = 0  is the exact solution. No iterations were performed.
vnl_lsqr.cxx : The iteration limit ITNLIM was reached.
vnl_lsqr.cxx : residual norm estimate = 3.24731
vnl_lsqr.cxx : result norm estimate   = 14.2702
vnl_lsqr.cxx : condition no. estimate = 106.047
vnl_lsqr.cxx : iterations             = 30



I guess residual norm estimate holds the key. Any ideas?

thanks
Dominique