Hello everybody, I just saw that there is some discussion about leastsq, and guessed that this is a good time to add some ideas. I have been working on an all-python fitter, which is just the minpack fitter translated to python. This is why I was bugging yall for the qr_multiply stuff, for those who remember. Having the fitter in python is quite useful, because this calling python from FORTRAN sometimes was ugly: most importantly because exceptions often didn't find their way through FORTRAN. I added some new stuff as well: if the fitted function realizes that it's parameters are running away, it may raise an InvalidParameter exception, and the fitting algorithm will choose a smaller step size on this parameter. You can find the code at https://github.com/scipy/scipy/pull/88 Greetings Martin