Subject:

**Solution preference or curvature of chi2**
Hi all,

I'm wondering if it's possible to work out the preference for a particular refinement solution? I think another way of putting this is that I want to know if it's possible to work out the curvature of chi2 with respect to a parameter (in the example below: composition)?

For example, consider a 2-phase refinement. Now, let's say that the refinement produces the lowest Rwp for 30%/70% mix. Now, what if you tried repeating the refinement with various fixed compositions (increment by 5% between the two in a batch script) and you found that the Rwp was still lowest for the 30/70 mix, but the Rwp was almost the same for each of them (i.e. a plot of Rwp vs comp% would almost be flat line). From this you could say there's no real preference for the best solution (not sure if "preference" is the correct term or not...).

Now let's say for another 2 phase refinement you have the exact same process, but this time there's actually a (upside down) peak when you do a plot of Rwp vs comp%. Hence, you can confidently say that the result with the minimum Rwp is the best result.

Feel free to correct my terminology.

Thanks,

Fred

I'm wondering if it's possible to work out the preference for a particular refinement solution? I think another way of putting this is that I want to know if it's possible to work out the curvature of chi2 with respect to a parameter (in the example below: composition)?

For example, consider a 2-phase refinement. Now, let's say that the refinement produces the lowest Rwp for 30%/70% mix. Now, what if you tried repeating the refinement with various fixed compositions (increment by 5% between the two in a batch script) and you found that the Rwp was still lowest for the 30/70 mix, but the Rwp was almost the same for each of them (i.e. a plot of Rwp vs comp% would almost be flat line). From this you could say there's no real preference for the best solution (not sure if "preference" is the correct term or not...).

Now let's say for another 2 phase refinement you have the exact same process, but this time there's actually a (upside down) peak when you do a plot of Rwp vs comp%. Hence, you can confidently say that the result with the minimum Rwp is the best result.

Feel free to correct my terminology.

Thanks,

Fred