# How to solve 'User supplied objective function must return a scalar value' in fmincon?

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Arifur Rahman on 27 Jan 2018
Answered: Walter Roberson on 28 Jan 2018
Hello. I have done power flow calculation. After power flow calculation, I got Losses in the line which is (131x96) matrix. This matrix I have used as an objective value to optimize losses. The objective value is like below,
AC_DC_losses=abs(LineLosses); ----- (131x96) matrix.
When I optimize with fmincon, it shows the error like, 'User supplied objective function must return a scalar value'. I am understanding the problem. Is this the problem because the objective value is (131x96) matrix. Could anyone give me suggestion regarding this?
Walter Roberson on 27 Jan 2018
You have multiple outputs. What are you trying to optimize:
• minimize total losses?
• minimize median loss?
• minimize standard deviation of losses?
• find a set of losses such that it is not possible to lower any one of them without raising at least one other of them? ("Pareto front")

Walter Roberson on 28 Jan 2018
To minimize total losses your output should be
AC_DC_losses = sum(abs(LineLosses(:)));

Arifur Rahman on 27 Jan 2018
I have to minimize total losses. @Walter Roberson