issorted alternative for optimization toolbox

Question

Kendall Knight 2019-2-20

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https://ww2.mathworks.cn/matlabcentral/answers/446037-issorted-alternative-for-optimization-toolbox

编辑： Matt J 2019-2-20

I have an optimvar A that needs to be constrained to be in descending order. The code

sorted = issorted(A,'descend') == 1;
prob.Constraints.sorted = sorted;

returns "Error using issorted. Undefined function 'issorted' for input arguments of type 'optim.problemdef.OptimizationVariable'."

Is there an alternative to 'issorted' to implement this constraint?

Thanks

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Answer 1

Matt J 2019-2-20

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https://ww2.mathworks.cn/matlabcentral/answers/446037-issorted-alternative-for-optimization-toolbox#answer_361910

编辑：Matt J 2019-2-20

在 MATLAB Online 中打开

You can do,

prob.Constraints.sorted = ( A(2:end) <= A(1:end-1) );

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Answer 2

John D'Errico 2019-2-20

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Apparently not. However, you don't need it either. What stops you from just using a cumulative sum? Then constrain all elements of the vector but the first to be negative? The net result is you will have a decreasing sequence.

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Kendall Knight 2019-2-20

编辑：Kendall Knight 2019-2-20

You're right. I did not think of that solution. The issue is the variable array is then mulitplied by a postive constant array and the total sum of the element wise multiplication of those two arrays is the minimiation objective. Because of this objective, constraining all but the first entry to be negative leads to the first entry taking on an unrealistic positive value due to the physical nature of the problem.

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