Retrieve loop counter values in nested loop, and plotting specific calculation

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Pit Probst 2018-8-14

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评论： dpb 2018-8-15

Hello all. My questions are as commentated

count = 0 ;
vec = zeros([],7) ;
for a=1:3
  A= 2*a ;
  for b=a+1:6 
      B=3*b ;
      for c=b+1:10
          C=4*c ;
         count = count+1 ;
         total=sum([A B C])
          vec(count,:)=[a b c A B C total]; 
      end
   end
end 
value = max(total)       % get max and return values of a,b,c when this happens
                         % plotting corresponding individual calculation A B C for the max(total)
end

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Pit Probst 2018-8-15

编辑：Pit Probst 2018-8-15

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Hi, sorry for the ambiguity. With example : we can take this as a bag of nuts-mix being maximized for profits. loop counter represent the maximum constraint i.e max 3 units of type a, max 5 of type b and remainder of type c. updated the loop counter to reflect this

A, B, C are the resulting profits.

say, the maximum profit = 74 and it occurs at a=2, b=3,c=5. Then corresponding values for A= [2 4], B= [3 6 9] and C= [5 10 15 20] I want to plot this as a vector= [2 4 3 6 9 5 10 15 20].

If all values are stored as a matrix, at the end of each loop iteration, then it is possible to extract the elements (and any other just as well), and get a full picture - I unable to do this. All of it.

here is my code with updated loop counters:

 count = 1 ;
vec = zeros([],11) ;
for a=1:3
  A= 2*a ;
  for b=a+1:6 
      B=3*(1:b) ;
      for c=b+1:10
          C=4*(1:c) ;
         total=sum([A B C]);
          vec(count,:)=[a b c A B C total]. % gave a you have 10 on LHS but 11 on RHS , assignment error
          count = count+1 ;
      end
   end
end 
value = max(total);   
  end

Adam Danz 2018-8-15

在 MATLAB Online 中打开

I don't follow your explanation. However, when I run your code I get an error on the first iteration since

[a b c A B C total]

has 10 elements but

vec(count,:)

expects 11 elements. On the 2nd iteration there are 11 elements in [a b c...] so there isn't an error.

Pit Probst 2018-8-15

编辑：Pit Probst 2018-8-15

在 MATLAB Online 中打开

say,max(total) = 74. So the output of the code should be/needs to be:

 value=74
a=2
b=3
c=5
A= [2 4]
B= [3 6 9]
C= [5 10 15 20]
vec = [A B C]

or: store each output of each iteration as new row in a matrix

vec=[a b c A B C value]

so vec=[2 4 3 6 9 5 10 15 20], and I can plot vec. I am somehow not storing the iterations correctly. Hence cannot retrieve values nor plot...

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Answer 1

dpb 2018-8-15

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https://ww2.mathworks.cn/matlabcentral/answers/414888-retrieve-loop-counter-values-in-nested-loop-and-plotting-specific-calculation#answer_332863

编辑：dpb 2018-8-15

在 MATLAB Online 中打开

I didn't notice the "growing" of the vector length...you've got to use a cell array to handle that.

total=[]; vec=[];
count=0;
for a=1:3
  A= 2*a ;
  for b=a+1:6 
    B=3*(1:b);
    for c=b+1:10
      C=4*(1:c);
      count=count+1 ;
      total(count)=sum([A B C]);
      vec{count,1}=[sum([A B C]) a b c A B C];  % make column cell array
    end
  end
end 
[value,ival]=max(total);

To retrieve the content use

vec{ival}

NB: that with the given positive value the maximum is always the last value so there's no need to search; one presumes this is artificial example.

One could also do the max() on the running total in the loop; there's no real reason to save anything except the maximum and conditions so far to get the actual result

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Pit Probst 2018-8-15

编辑：Pit Probst 2018-8-15

Going back to your first code. vec{ival} works ! - and ill go with that. And yes, this code is an artificial example and part of a larger code in optimization. I can't post the real equations due to confidentiality. I can see why you'd think this the max value is a no-brainer as it is obviously at the end - didn't spend too much time dressing the equations.

The example immediately above was manually calculated while typing, to demonstrate the rationale for the problem. that's all.

Thanks for all your inputs! I was slightly pre-stressed about retrieving values, and missed the vec{ival}. But thanks a ton! I'll to do better!

dpb 2018-8-15

OK...if wish, post a new Q? that illustrates your final output storage arrangement and what you want to retrieve and we can address the efficiencies regarding what, specifically, to actually store and how to retrieve what's needed for the real application.

I just introduced the total vector as an intermediary device to get to an answer while still trying to define the problem.

If it's so that you do want/need the subvectors then I recommend the probably solution is to save 2D cell array instead of 1D array of variable-length vector that combines the different pieces.

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Retrieve loop counter values in nested loop, and plotting specific calculation

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