fsolve function working at times but failing sometimes! Warning on non-square systems!

Hello, Would somebody please explain to me why is that I sometimes get the following warning:

" Trust-region-dogleg algorithm of FSOLVE cannot handle non-square systems; using Levenberg-Marquardt algorithm instead. "

I get an answer many other times without getting this warning, but 'sometimes' I get NaN as an answer along with this warning! This is while the code is exactly the same each time.

I am solving two non-linear equations in my program each time. This warning is related to fsolve function I use for solving those equations. Why is that this function sometimes fails but works the other times without any change in the code?!?

I would be grateful if somebody explain this to me as it makes my program very unreliable.

Thank you. Atekeh

[Matt J]

Is it possible you sometimes have more than 2 unknown variables?

[Atekeh]

Hi, No! It's always two unknown variables to be solved and the other input parameters to the MATLAB function (where fsolve is called) are always the same! Thanks.

[Matt J]

Don't think so. If fsolve thinks you have a non-square system, you have different numbers of equations from variables at some point.

[Atekeh]

Not that of I know! I swear I have only two equations in my code. That's weird! And as I said, most of the time it runs and there is no such error/warning and I get the answer! How is that the same code, with the same set of parameters passed to it, runs but fails sometimes?! Thanks anyway.

[Matt J]

Without seeing your code, we cannot know. Maybe you have rand()-driven lines somewhere...

[Atekeh]

Oh the code is so long and nested that is not easy to look at. No, I don't have rand() function in my code. I appreciate your efforts to help though. Thanks.