# Negative parameters **URL:** \ **Category:** Modelling and Simulation\ **Created:** [July 17, 2013, 2:00pm UTC](https://forum.certara.com/t/negative-parameters/2596 "2013-07-17T14:00:32Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![bhargav\_1](https://avatars.discourse-cdn.com/v4/letter/b/958977/32.png) [@bhargav\_1](https://forum.certara.com/u/bhargav_1)\ **Post date:** [July 17, 2013, 2:00pm UTC](https://forum.certara.com/t/negative-parameters/2596/1 "2013-07-17T14:00:32Z")
Hi, I have recently obtained negative parameters when modeling and was wondering what PHX is trying to tell with this output? Usually it is the elimination rate constant Ke in the closed form two compartment models that acts up. Obviously there is an error but is it due to a local minimum or maybe the model just can’t fit the data and another model has to be considered? I would like to know because it has happened fairly often lately. Best regards, Yassine ---
**Author:** ![minhaj](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@minhaj](https://forum.certara.com/u/minhaj)\ **Post date:** [July 17, 2013, 3:09pm UTC](https://forum.certara.com/t/negative-parameters/2596/2 "2013-07-17T15:09:50Z")
Dear Yassine The best way to avoid that is just to put 0 lower boundaries in the fixed effects tab. This will prevent this to happen. Try it and let me know. I am not sure it is a local minimum but it can happen but of course this is wrong. best Serge ---
**Author:** ![bhargav\_1](https://avatars.discourse-cdn.com/v4/letter/b/958977/32.png) [@bhargav\_1](https://forum.certara.com/u/bhargav_1)\ **Post date:** [July 19, 2013, 9:17am UTC](https://forum.certara.com/t/negative-parameters/2596/3 "2013-07-19T09:17:17Z")
Hi Serge, After performing the fixed effects lower bound 0 the model now has only positive parameters. I appreciate your help. Yassine