Performing calculation with multiple conditions with for loop and nested if statements

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Kevin Zhang 2017-12-4

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评论： Kevin Zhang 2017-12-5

I have a column of data (temperatures) and want to create a second column based on these temperatures. In Excel, it is accomplished with a simple nested if statement. My loop in Matlab, however, works for a few rows, then begins to return 0's. The conditions are:

If temperature (T1) is < 0, then RHCrit = 0
If T1 is between 0 and 20, then RHCrit = -0.00267*(T1^3)+0.160*(T1^2)-3.13*T1+100
If T1 is >20, then RHCrit = 80

My code right now is:

RHcrit = zeros(size(T1));
  for i = 1:length(T1)
      if T1(i)>0
          if T1(i)<20
              RHcrit(i)=-0.00267*(T1(i)^3)+0.160*(T1(i)^2)-3.13*T1(i)+100
          else
              RHcrit(i)=80
          end
      else
          RHcrit(i)=0
      end
  end

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Nicolas Schmit 2017-12-5

Please share the value of T1 so that your code can be tested.

Kevin Zhang 2017-12-5

Hi Nicolas,

Apologies, a .txt file is attached.

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Answer 1

Nicolas Schmit 2017-12-5

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https://ww2.mathworks.cn/matlabcentral/answers/371027-performing-calculation-with-multiple-conditions-with-for-loop-and-nested-if-statements#answer_294694

在 MATLAB Online 中打开

This code is working fine. Are your sure you loaded T1 properly? As KSSV mentioned, you do not need a for loop to do this calculation. Using logical indexing would be more efficient.

ds = datastore('T1.txt');
data = ds.readall();
T1 = data{:,1};
RHcrit = zeros(size(T1));
  for i = 1:length(T1)
      if T1(i)>0
          if T1(i)<20
              RHcrit(i)=-0.00267*(T1(i)^3)+0.160*(T1(i)^2)-3.13*T1(i)+100;
          else
              RHcrit(i)=80;
          end
      else
          RHcrit(i)=0;
      end
  end

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Kevin Zhang 2017-12-5

Okay, I think there was a bug with my original file. I copied the file retrieval portion and appended the for loop, in a new file, and it worked fine. Something was wrong with the original file I was working in.

Kevin Zhang 2017-12-5

I am an idiot. I didn't add semicolons to the statements in my for/if loops. This was what was causing all of my problems.

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Performing calculation with multiple conditions with for loop and nested if statements

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