If fitting a fairly sparse data set it’s often nice to plot a smooth fit curve through the points (i.e. evaluating the function at more X values). It can often reveal mistakes in the function or initial parameters such as a sharp peak being located where there aren’t any data points at all, or a rapid oscillation only sampled once per few cycles. Some other programs such as Origin have this as an option in their fitting routines. Could we have the option to do it in Mantid’s fit interface? A “work around” is possible by changing the data set to one I prepared earlier with the desired X values, fixing parameters, re-running Fit or Plot Guess, and manually overlaying curves, but that’s not so useful when working out why my fit doesn’t make sense and which parameter to change.

A suggested change to the interface would be to have a check box “Plot fit curve at uniform X” and a numeric entry for the number of points (e.g. 200). Points could be equally spaced between StartX and EndX.

Obviously the fit itself (and the difference plot if requested) must still use just the X values in the data. Composite Members curves would also be at the uniform finely spaced X values.