try to keep track of the plot in a loop? how to do that?

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William 2014-3-8

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https://ww2.mathworks.cn/matlabcentral/answers/120717-try-to-keep-track-of-the-plot-in-a-loop-how-to-do-that

评论： William 2014-3-10

%what I am doing here is to generate series of matrices, and multiply them together, but i want to keep track of the matrix elements, i might use the plot wrong, or how to do that? can anyone help me? I am a starter of coding, thank you!

function MonodromyM
double q
syms x
V(x)=(1/sqrt(2*pi))*(1/0.5)*exp((-x^2)/(2*0.5^2));
V2(x)=diff(x,2);
M=[1 0;0 1];
for i=1:1000
      q=2*pi*rand(1);
      A=[1 1;-V2(q) 1-V2(q)];
      M=M*A;
      hold on
      fprintf('%d\n', M(1,1))
      fprintf('%d\n', M(1,2))
      fprintf('%d\n', M(2,1))
      fprintf('%d\n', M(2,2))
end

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Answer 1

Mischa Kim 2014-3-9

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https://ww2.mathworks.cn/matlabcentral/answers/120717-try-to-keep-track-of-the-plot-in-a-loop-how-to-do-that#answer_127584

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William, a couple of things. See inlined comments:

 function M = MonodromyM()    % M is outputted by function and available for further
                              % ...analysis, for example in the MATLAB command window
 syms x
 V  = (1/sqrt(2*pi))*(1/0.5)*exp((-x^2)/(2*0.5^2));
 V2 = diff(V,2);              % Did you mean to compute the 2nd deriv. of V?
 M(:,:,1)=[1 0;0 1];
 for i  = 1:10
     q  = 2*pi*rand(1);
     V2 = subs(V2,x,q);       % substitute x by current value for q
     A  = [1 1;-V2 1-V2];
     M(:,:,i+1) = M(:,:,i)*A; % save values of M in a 3D array
     %       hold on
     %       fprintf('%d\n', M(1,1))
     %       fprintf('%d\n', M(1,2))
     %       fprintf('%d\n', M(2,1))
     %       fprintf('%d\n', M(2,2))
 end