This is something noted by Ian Silverwood, but I’ve had a few similar issues in the past.
I’m just getting started with peak fitting, but I’m having trouble and the data seem to be misbehaving so I’m wondering if it is a bug.
Using the fitting wizard as described in Spencer’s fitting primer seems to be going OK, but if I try a sequential fit, it gives me the error:
Error in execution of algorithm PlotPeakByLogValue:
bad lexical cast: source type value could not be interpreted as target
This was fitting the reduction of 26176 with the resolution created from 26173 on IRIS (a standard set of test data for QENS at ISIS) with a fit function similar to what ConvFit does in 2 Lorentzian mode (with no background function).
Ian was using 3:12 as the input in the Spectra column in the Sequential Fit interface with Output Composite Members and Convolve Members enabled, and reports that disabling Output Composite Members and Convolve Members fixes the issue.
I tried with a very basic fit of a single Lorentizian to the same data and found that any input in the Spectra column gave the same error, using the Range column seems to work fine.
In the end I just recommended using the Multi Dataset Fit interface for fitting multiple spectra.