Complex Mode Shapes from FRF

I have been trying to implement an MDOF fit with MATLAB but I am having a hard time.

The problem is that you do not give estimated values to MATLAB, so when you use commands like 'modalfit' it does not replicate the initial FRF in a good way.

I tried also to create a continuous-time FRF by using 'tfest' and then extract the modal parameters from there, but not with great results.

MATLAB seems to use these algorithms ( like least squares rational fraction ) ignoring the residues because I have see narticles from people using them and getting much better reconstructions. I know my data is tricky because it is a beam with 23 points of measurement but I can not figure how to extract the complex mode shapes with good results.

If you could get me to some code or reference featuring these problems will be so much helpful for me.

Thank you.

[Tarsem Singh Khalsa]

Can you give some more detail and some theory of what you want to do?