mpfit: what's different

Hi everyone,

Is there any do***entation on the theory behind Craig Markwardt's
mpfit? What's different from the Levenberg-Marquardt algorithm as
given in "Numerical Recipes in C" (used in IDL's curvefit)?

Is it a difference in choosing the damping factor in the modified
curvature matrix or is there more to it?

Thanks,

Wout