> Having started to use the new version of PHREEQC (version 2) in an inverse modelling mode, I tried running old models (run on version 1.03 PHREEQCi) to check the feasible models were the same. Unfortunately I find that the number of feasible models produced in version 2 is always less. It looks like some of the reactions pass your 1e-7 tolerance in one version, but not the other. If you lower that tolerance (default is around 1e-10, I think), then the two versions give the same number of minimal models. I think the differences you are seeing are related to handling small numbers. The redox reactions that account for the differences are on the order of 1e-7. There may have been some changes in the way the equations were scaled between the two versions that accounts for the difference. If you are worried about the differences, which are on the order of 1e-7, then you need to use a smaller tolerance (this is not the uncertainty). If you do use a smaller tolerance, it looks like the two versions are consistent. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225
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