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

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?

Thanks in advance.

[Walter Roberson]

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")

Answer 1

[Walter Roberson]

To minimize total losses your output should be

AC_DC_losses = sum(abs(LineLosses(:)));

Answer 2

[Arifur Rahman]

I have to minimize total losses. @Walter Roberson