mapSolution broken in R2019b?

Question

Matt J 2020-8-15

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https://ww2.mathworks.cn/matlabcentral/answers/580044-mapsolution-broken-in-r2019b

评论： Matt J 2020-9-1

In R2019a, the following code works as intended,

           %% Define the variables
           x=optimvar('x',{'x1','x2'},'LowerBound',[-100,-200]);
           y=optimvar('y',1,3,'LowerBound',[0 0 0],'UpperBound',[+300,+400,+500]);
  
           %% Define some constraints
           C.inequ=2*sum(y)+sum(x)<=1000;
           C.equ=5*sum(x)==100;
            
           
           prob=optimproblem('Constraints',C,'Objective',sum(x)+sum(y));
           
           idx=mapSolution(prob,1:5)
           

resulting in the output,

    idx = 
    
      struct with fields:
    
        x: [1 2]
        y: [1 2 3]

Something must have been changed in R2019b/R2020a, however, because I instead get an error:

    Not enough input arguments.
    
    Error in optim.internal.problemdef.ProblemImpl/mapSolution
    
    Error in test (line 12)
               idx=mapSolution(prob,1:5)

Were there any intentional changes in the behavior of the mapSolution function, and if so how do I get the code above to work in current Matlab?

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Matt J 2020-8-16

There is a qualifying Note there, however, showing that certain subsets of the input argument list are allowable... Why would the two-input combination no longer be allowable based on what's written there, and considering also that it clearly did work in R2019a?

Walter Roberson 2020-8-16

Darn, it is a .p file so we can't read it.

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Answer 1

Paul Kerr-Delworth 2020-8-28

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Hi Matt and Walter,

Firstly Matt, many apologies that you've run into this unintended behavior. Also, many thanks to you both for looking into this and flagging it up.

What has happened here? The short answer is that mapSolution was made an internal function in R2019a and replaced with varindex. Once we made mapSolution internal, we repurposed it in R2019b leading to the internal error you encountered. We will tidy up the error and add a note in the documentation pointing you to varindex

Matt's original code works with varindex

%% Define the variables
x=optimvar('x',{'x1','x2'},'LowerBound',[-100,-200]);
y=optimvar('y',1,3,'LowerBound',[0 0 0],'UpperBound',[+300,+400,+500]);
  
%% Define some constraints
C.inequ=2*sum(y)+sum(x)<=1000;
C.equ=5*sum(x)==100;
            
           
prob=optimproblem('Constraints',C,'Objective',sum(x)+sum(y));
idx = varindex(prob);

Resulting in the output

idx = 
  struct with fields:
    x: [1 2]
    y: [3 4 5]

Also, varindex allows you to get the variable index by name, e.g.

idx = varindex(prob, 'y')

Resulting a double as the output

idx =
     3     4     5

Matt, may I ask if you were aware of varindex? Also, is there anything in mapSolution that you are relying on that varindex doesn't provide?

Thanks again for flagging this and hope varindex helps!

Cheers,

Paul

Documentation for varindex:

https://uk.mathworks.com/help/optim/ug/optim.problemdef.optimizationproblem.varindex.html

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Paul Kerr-Delworth 2020-9-1

编辑：Paul Kerr-Delworth 2020-9-1

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Hi Matt,

Many thanks for the clarification, that's really helpful for us.

For a backwards compatible solution that can work, you can add your own version of varindex to the path as a separate function

function solstruct = varindex(prob)
if ~isa(prob, 'optim.problemdef.OptimizationProblem')
    error('First input to VARINDEX must be an OptimizationProblem');
end
if verLessThan('matlab', '9.6')
    error('This function is intended for R2017b - R2018b. Make this a separate function on the path.')
end
N = sum(structfun(@numel, prob.Variables));
solstruct = mapSolution(prob, 1:N);
end

Now for R2017b-R2018b, this function will be called as varindex doesn't exist. From 19a onwards the shipping OptimizationProblem method will be called as it is higher in the precedence order than your varindex.

https://uk.mathworks.com/help/matlab/matlab_prog/function-precedence-order.html

Would you be happy to move to varindex with this solution?

Cheers.

Paul

Matt J 2020-9-1

Thanks,Paul. That looks great. And yes, varindex is what I would use.

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Answer 2

Matt J 2020-8-17

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https://ww2.mathworks.cn/matlabcentral/answers/580044-mapsolution-broken-in-r2019b#answer_481224

编辑：Matt J 2020-8-25

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This seems to be a simple work-around,

idx=mapSolution(prob,1:5,[],[],[],[],[])

but I can't help wondering if it's really supposed to be required. It is very uncharacteristic of TMW-supplied commands to require trailing [] input arguments.