Double Summation expression in Objective Function

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Hi Experts, I have a Parameter matrix, C of size 2x2. It looks like this.
C= [2 4; 6 8]
I have a decision variable, X of size 2x2. It looks like this
[ X('S1', 'D1') X('S1', 'D2') ]
[ X('S2', 'D1') X('S2', 'D2') ]
I want to formulate my Objective Function as a series of double expression (Please refer the attachment),
Which shall look like the following after the expansion.
Z = 2*X('S1', 'D1') + 4*X('S1', 'D2') + 6*X('S2', 'D1') + 8*X('S2', 'D2')
I try the following.
Z = sum(C.*X,1);
But it creates An optimizationExpression of size 1x3, which is not desired.
What am I doing wrong? Is there any easier way to do so without using for loop. I have just started learning "Problem-Based Optimization" in MATLAB today. Any help will be greatly appreciated.

Accepted Answer

Mary Fenelon
Mary Fenelon on 5 Sep 2018
Was it a 1x3 OptimizationExpression or 1x2?
In any case, you need to sum over both dimensions to get a single OptimizationExpression
Z = sum(sum(C.*X))
  2 Comments
pradeep kumar
pradeep kumar on 5 Sep 2018
@ Mary Fenelon, Thanks for your solution. It should be actually 1x2 OptimizationExpression, Sorry for my typing mistake. Could you please explain me the logic behind this? I have triple summation and more expressions in the future prob lem.Thanks in advance!
Mary Fenelon
Mary Fenelon on 5 Sep 2018
Look here for documentation on the sum function. This example has a 3 dimensional OptimizationVariable.

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