# Problem with soft constraints in RBDO **URL:** \ **Category:** Community Q&A and How To\ **Tags:** rbdo\ **Created:** [July 3, 2020, 3:39pm UTC](https://uqworld.org/t/problem-with-soft-constraints-in-rbdo/718 "2020-07-03T15:39:30Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Soheil\_Radfar](https://uqworld.org/user_avatar/uqworld.org/soheil_radfar/32/460_2.png) [@Soheil\_Radfar](https://uqworld.org/u/Soheil_Radfar)\ **Post date:** [July 3, 2020, 3:39pm UTC](https://uqworld.org/t/problem-with-soft-constraints-in-rbdo/718/1 "2020-07-03T15:39:30Z")
Hello everyone Following my previous questions on implementing the RBDO problem, I have trouble defining soft constraints. We know that in an optimization problem, in addition to the inequality constraints, there are also **equality constraints**. But I don’t know how to define such constraints? Also, in one of my soft constraints, the **MATLAB max function** is used, but there is a problem with this part when running the program. I have attached the MATLAB codes and I have specified these constraints in “uq\_RubBreakwat\_SoftCon.m” as comments. **Does anyone have a suggestion to solve this problem?** **The zip version of all code files is also attached.** [RBDO.zip](https://uqworld.org/uploads/short-url/bPnMG6xngE1rNJM0ioa86UXgMPP.zip) (3.6 KB) ---
**Author:** ![moustapha](https://uqworld.org/user_avatar/uqworld.org/moustapha/32/226_2.png) [@moustapha](https://uqworld.org/u/moustapha)\ **Post date:** [July 17, 2020, 9:37am UTC](https://uqworld.org/t/problem-with-soft-constraints-in-rbdo/718/2 "2020-07-17T09:37:57Z")
Hi @Soheil_Radfar Unfortunately equality constraints are not supported in the current version of the RBDO module. I would however suggest the following two options: 1. Define two inequality constraints to form an equalitiy one e.g. X \<= a and X \>= a. I am not sure if the algorithm would perform well with such a trick though. It’s probably not the best approach but may be it will help. 2. Alternatively, I would suggest you hard-code your equality constraints in UQLab. If you are using an `fmincon`-based solver, you can go in the file uq\_matlabnonlconwrapper.m and add the constraint directly at the end of the file. At line 67, you will see `ceq = [];` You can then write your equality soft constraints there a few lines above and save the result (as a row vector if you have many) in the variable `ceq` which will then be carried out in `fmincon` as equality constraint. Regarding the max constraint, I am not sure what you actually tried to achieve. Your max constraint has three arguments, two of which are constant. So you can simply remove the smallest of the two: This `Y(:,17) = max(2 .* X(:,13), 0.4 * 4.91, 3 * 0.384) - X(:,9)` becomes this `Y(:,17) = max(2 .* X(:,13), 0.4 * 4.91) - X(:,9)` … or may be I am mistaken you were trying to do something else. In any case, the `max` function does not take three arguments. If you have more than two arguments, you need to put everything in a single matrix and then use the max operator in the appropriate dimension. Cheers, Moustapha ---
**Author:** ![Soheil\_Radfar](https://uqworld.org/user_avatar/uqworld.org/soheil_radfar/32/460_2.png) [@Soheil\_Radfar](https://uqworld.org/u/Soheil_Radfar)\ **Post date:** [July 17, 2020, 4:35pm UTC](https://uqworld.org/t/problem-with-soft-constraints-in-rbdo/718/3 "2020-07-17T16:35:27Z")
Dear @moustapha As always, your solutions are very effective. I checked the first proposed solution and the answers were obtained with a very good approximation. Thank you very much. ---
**Author:** ![damarginal](https://uqworld.org/user_avatar/uqworld.org/damarginal/32/73_2.png) [@damarginal](https://uqworld.org/u/damarginal)\ **Post date:** [July 17, 2020, 6:02pm UTC](https://uqworld.org/t/problem-with-soft-constraints-in-rbdo/718/4 "2020-07-17T18:02:24Z")