Problem in executing a for loop

Question

Sai 2015-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/243249-problem-in-executing-a-for-loop

评论： Walter Roberson 2015-9-16

I'm trying to filter data for Quadrant hole analysis. My intention is to calculate total sum (S_Q1_H) for each H-value which I'm trying to implement via a for loop initiated at the beginning as for H=1:4 Even though the code is being executed, the output shows that all the 4 values of total sum S_Q1_H are same

No matter how many times I check, I'm unable to find where the logic error is... Here is the code.

for H=1:4 
temp=0;
for n = 1:1000000
     sprintf('%f',H);
  if and(u_real(n)>0,v_real(n)>0)
      if n == temp + 1
          u_Q1(n) = u_real(n);
          v_Q1(n) = v_real(n);
          if ((u_Q1(n)*v_Q1(n))> (H*s_U*s_V))
              u_Q1_H(n)= u_Q1(n);
              v_Q1_H(n)= v_Q1(n);
          end
          temp = n;
      elseif n~= temp+1
          d = n-temp;
          u_Q1(n) = u_real(n);
          v_Q1(n) = v_real(n);
          if ((u_Q1(n)*v_Q1(n))> (H*s_U*s_V))
              u_Q1_H(n)= u_Q1(n);
              v_Q1_H(n)= v_Q1(n);
          end
          temp = n-d+1;
      end
  end
end
u_Q1_H_s = u_Q1_H(u_Q1_H~=0);
v_Q1_H_s = v_Q1_H(v_Q1_H~=0);
[f,s1]=size(u_Q1_H_s);
temp=0;
for o=1:s1
     S_Q1_H(H) = temp + u_Q1_H_s(o)*v_Q1_H_s(o);
     temp = S_Q1_H(H);
     S_avg_Q1(H) = temp/o;
end
end

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Sai 2015-9-16

编辑：Walter Roberson 2015-9-16

在 MATLAB Online 中打开

Can anyone tell me the syntax to create a new variable in each iteration of for loop

for H=1:4
          if ((u_Q1(n)*v_Q1(n))> (H*s_U*s_V))
              u_Q1_H'num2str(H)'(n)= u_Q1(n);
              v_Q1_H'num2str(H)'(n)= v_Q1(n);
          end
end

My aim is to create u_Q1_H1(n) for H=1, u_Q1_H2(n) for H=2...and so on...

Walter Roberson 2015-9-16

Don't do that!

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

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Answer 1

Walter Roberson 2015-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/243249-problem-in-executing-a-for-loop#answer_192519

在 MATLAB Online 中打开

Inside your "for n" loop you have

if n == temp + 1

but you have not initialized temp in the given code before you use it here.

If you do happen to have an initialized temp before starting the loop, then note that the next H along, the temp value will be temp = S_Q1_H(H); from the "for o" loop. It seems unlike that is what you want.

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Sai 2015-9-16

编辑：Sai 2015-9-16

Thanks for your answer, Yes, I do have a 'temp' initialized before that..and after the 'for o' loop But, I still observe the output is same for all the 4 values. After the first iteration it, seems the 'for n' loop isn't executing. Struggling to find the answer

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Answer 2

Guillaume 2015-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/243249-problem-in-executing-a-for-loop#answer_192522

编辑：Guillaume 2015-9-16

The best way for you to understand why your program is not giving you the correct result is to use the debugger. Place a breakpoint on the first line of code, step through each line and observe the result of each operation as it is executed. You'll quickly see if your loop is executed and if not, why not.