I am having a problem using Minuit with PyRoot. I have a working fitting application and am now trying to add calculated derivatives to my fcn.
The argument list for fcn, called from inside Minuit, is:
def chisq( npar, gin, f, par, iflag ):
but when I try to set the value of gin (thats the gradient) I get an error:
gin = theValueOfMyDerivative
TypeError: ‘bad argument type for built-in operation’
(I notice that gin has an unusual type, ROOT.PyDoubleBuffer, while f, the thing being minimized, is a python list.) So the question is: how can I change the values of gin?