# Lsqnonlin with nonlinear constraint!

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GMark on 6 Sep 2015
Commented: GMark on 8 Sep 2015
Dear Community, I need to use a nonlinear constraint with the "lsqnonlin" optimization algorithm. To apply the constraint I am using the following procedure. FF = myfunction(pars). In myfunction I use the IF statement as follows: IF "nonlin constraints are respected" then compute FF ELSE FF=10e100 END. In other words, I make the objective function very large if the constraint is not respected, making the algorithm search for other parameters. Since I do not know how the algorithm works, is this a feasible solution? Thanks

Alan Weiss on 8 Sep 2015
It seems to me that you have a nonlinear constraint with a sum of squares problem. If you examine the Optimization Decision Table, you see that you should use fmincon, not lsqnonlin. Rewrite the objective function for fmincon so that it is a sum of squares, F'*F if F is a column vector of the components of the lsqnonlin objective function.
And no, it is not a good idea to have a non-smooth objective function that takes an arbitrary large value for infeasible points.
Alan Weiss
MATLAB mathematical toolbox documentation

#### 1 Comment

GMark on 8 Sep 2015
Hi Alan, thanks a lot for responding. This is exactly the answer I wanted. I am already using fmincon and the on-website function fminsearchcon to double check my optimization. I wanted to use lsqnonlin as an extra tool, but I kind of realized it was not a good idea to break the function for non-feasible parameters. Thanks a lot