inverse not converged

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T ze
Posts: 5
Joined: Wed Feb 27, 2019 11:28 am
Location: China

inverse not converged

Post by T ze » Sun Mar 10, 2019 12:48 pm

Hello,
I want to inverse the parameter n in the VG equation for the deep soil layer with the measured soil water content, but sometimes it will show that it is not converged. So, I am not sure how to adjust modify the setting in th hydrus, the detail information in the hydrus is below.
Hope for your suggestion, thanks!
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Jirka
Posts: 4787
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: inverse not converged

Post by Jirka » Sun Mar 10, 2019 7:12 pm

First of all, I think that it is unrealistic to try to fit 14 parameters (the n parameter for 14 soil layers) when you have only the final time water content profile. You should check out some literature on inverse parameter estimation, e.g.,

Šimůnek, J., and J. W. Hopmans, Parameter Optimization and Nonlinear Fitting, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 1.7, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 139-157, 2002.
https://www.pc-progress.com/Documents/J ... apt1-7.pdf

Hopmans, J. W., J. Šimůnek, N. Romano, and W. Durner, Inverse Modeling of Transient Water Flow, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 3.6.2, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 963-1008, 2002.
https://www.pc-progress.com/Documents/J ... t3-6-2.pdf

However, if you proceed with the fitting anyway, you need to set the minimum constrain on the n parameters larger than 1, e.g., 1.05 or 1.1. If you have n parameters lower than 1.1, you should use the VG model with the air-entry value of 2 cm.

J.

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