The error 'Matrix dimensions must agree' during optimization.How can it be solved?

Question

Nitin Samuel 2013-1-8

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I have the following code where 'Ymeas' is an array of measured values and must be fitted with estimated values-'Yest' meanwhile optimizing K1 using an ode.The objective function is the sum of squares of difference b/w Ymeas and Yest. Ymeas and Yest are 11X2 arrays. It optimizes for a while and then the following error is shown:

'Matrix dimensions must agree.'

 function optimize
 [K1] = deal(3.5); 
 Ymeas = [
         1  1
        0.8696  0.8696
        0.7692  0.7692
        0.6897  0.6897
        0.625  0.625
        0.5714  0.5714
        0.5263  0.5263
        0.4878  0.4878
        0.4545  0.4545
        0.4255  0.4255
        0.4  0.4     ];
 T=[0:10:100];
 A0=Ymeas(1,1);
 B0=Ymeas(1,2);
 figure;
 plot(T,Ymeas);
 hold on;
 h = plot(T,Ymeas,'k','linewidth',2);
 minERR = Inf;
 opts = optimset('fminunc');
 opts.LargeScale = 'off';
 Xest = fminunc(@(X)objfun(X),[0],opts);
 Xest = num2cell(Xest);
 [K1] = deal(Xest{:}),
           function ERR = objfun(X);
               X = num2cell(X);
              [K1] = deal(X{:});
   [T,Yest] = ode45(@(t,y)[-K1*y(1)*y(2); 
                           -K1*y(1)*y(2)],[T],[A0,B0]);
              ERR = sum((Ymeas(:) - Yest(:)).^2);
              if ERR < minERR
                  minERR = ERR;
                  for n = 1:2; set(h(n),'Ydata',Yest(:,n)); end
                  drawnow;
              end;
          end;
  end

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Walter Roberson 2013-1-8

在 MATLAB Online 中打开

What are you expecting from your line

[K1] = deal(X{:});

The only point of that I can see at the moment is to issue an error message if X was not a scalar.

Nitin Samuel 2013-1-8

oh..but even without that , how can there be a problem with the matrix dimensions? Dimensions of both Ymeas and Yest are constant and only the values of Yest change...So why exactly is there an issue with the dimensions? Thanks...

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Answer 1

Teja Muppirala 2013-1-8

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The problem occurs when K1 is negative. The ODE solver blows up before it can integrate to all your time values. You should specify a constraint that forces K1 to be >= 0. For example, you might use FMINCON instead of FMINUNC.