For loop repetition question

Question

Todd 2013-11-29

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回答： Roger Stafford 2013-11-29

Hey guys, I'm trying to make my code below to give me N=1:10 (repeating the for loop 10 times) in addition to 1:20 and 1:50, do I need to make separate for loops for this or is there some way to get the current loop to give me this information?

 clear;
x0=[42;0;95];
extinct=0;
W=zeros(1,200);
for N=[1:10]
    F=2*rand(1)
    for t=1:200;
    W(t)=F;
    A=[0 0 F; .6 0 0; 0 .75 .55];       
    x=(A^t)*x0;
        if (sum(x)<1);
            extinct=extinct+1;
            break;
        end
    end
end
fprintf('Number of extinction events:%d\n',extinct)

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Answer 1

Image Analyst 2013-11-29

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在 MATLAB Online 中打开

You don't need the brackets, by the way. You'd need to wrap that whole loop in another loop to handle the other top values of N:

upperN = [10,20,50]
for k = upperN
  fprintf('Upper N = %d\n', k);
  for n = 1 : k
    fprintf('      n = %d\n', n);
  end
end

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Answer 2

Roger Stafford 2013-11-29

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Are you certain you want matrix power in A^t rather than element-wise power as in A.^t? Either way, your coding can be made more efficient in my opinion. Also what is the point of W(t) here. It gets repeatedly erased in subsequent passes through the outer loop - that is, for each subsequent value of N the array W is overwritten, or at least partially so.