YellProgram / Yell

Yell is a program for diffuse scattering interpretation using the 3D-∆PDF refinement.
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Look at weak eigenvectors of covariance matrix #30

Open aglie opened 9 years ago

aglie commented 9 years ago

It is very helpful to show which parameters (collectively) affect the R-factor the strongest and weakest. Those can be obtained using svd of the covatiance matrix:

U,s,V=svd(covariance_matrix)

Note however, the strangeness here:

V[0], V[1] - are the ones which affect the R-factor the least. V[N-2],V[N-1] - are the ones which affect the R-factor the most. V[N],V[N+1] - are the ones which DO NOT affect the R-factor (if exist).

This discontinuity is probably due to the nature of pseudo-inverse used to find the covariance matrix in levmar, and should be detected probably by the appropriate value of the eigenvalue.