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Posted 10 years ago by adacovsk
Hi!

So I am trying to estimate my flow flux boundary conditions via FePEST... I have flow going into the model and flow going out of the model and solving the inverse problem. However, since there is flux in/out we have negative values being written to the fpi file... I am thinking that negative values for ifm-implemented parameters in FePEST cannot be handled? I am using relative change limit. I'm not too good with this, so I don't know if it is a bug or my limited knowledge. :^)

Thanks,

Adam
Posted 10 years ago by Björn Kaiser
Parameters which can have negative values can be estimated by PEST. The only problem is, is that you cannot log transform them.

However there is a way to still use it. Set the initial value to a positive value. Then please make the lower and upper bounds positive, but set the SCALE option to -1. In this way, the parameter is set to the negative of its value, just before it is set to the FEFLOW model.

As log transforming a parameter is recommended you probably should do this.
Posted 10 years ago by adacovsk
Hi Björn, thanks for the suggestion, it's very clever! Never thought to scale by -1 and/or offset it!

Everything seems to be working, with a few minor hiccups. It seems that I am limited to a constraint of ~1e-8 for the flux and not smaller (really tiny model!). Also, I need to make 4 character names for the parameters or else scaling by -1 doesn't work? Might just be the delimiting causing an minor issue, oh well!

Thanks,

Adam

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