Drastic processing time between calling a function with a square root operation in it and simply writing the function in the script itself

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James 2013-6-17

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Hi,

Basically I encountered a very large change in processing time because of where I put a sqrt function. Here is the code:

for i = 1:Rows
      helloworld = i
      for k = 1:Columns
          for j = 1:OneExcelLength
       %       RO = DistanceFinder(DimLong(k),DimLat(i),OneLong(j),OneLat(j));
              RO = sqrt((DimLong(k) - OneLong(j))^2 + (DimLat(i) - OneLat(j))^2);
              if  RO < WellRadius
                  ScoreMatrix(i,k) = ScoreMatrix(i,k) + LogBOPD(j);
              end
            end
        end
    end

Here, I do the square root function in the script and it runs really fast. But if instead I take out hte comment and call a function where I wrote this same sqrt line and send it paramenters and it sends back an ouput, it seems to take probably about 1000 times as long... thats not an exaguration. I was wondering why this would be?

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Answer 1

Sean de Wolski 2013-6-17

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More than likely the matrix is preallocated in the script because it has run previously whereas the function creates a new workspace on each call.

Inside the function, do you have orange code analyzer warnings suggesting that the matrix changes size on every loop iteration?

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James 2013-6-17

在 MATLAB Online 中打开

The function is actually very simple and doesn't create a matrix at all... here it is: function[Distance] = DistanceFinder(LongOne,LatOne,LongTwo,LatTwo)

    Distance = 0;
    Distance = sqrt(((LongTwo - LongOne)^2 + (LatTwo - LatOne)^2));

end

The only difference between using the two different sets of code that I see is one calls a function while one just runs the exact same thing in the script and its actually 138 times slower to call the function.