how to have the final vector?

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Lilya 2020-3-29

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评论： Lilya 2020-3-29

Hi all,

I've written the following script to calculate the wind direction from u and v components, taking into consideration the quadrants.

The problem is that I should have the final vector for the plot.

Where am I mistaken?

Note: U10 and V10 have a dimension of (1*120).

Thanks for the help.

for i = 1:length (U10);
  if(V10 > 0)   
      kk = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 180);
  elseif (U10 < 0 & V10 < 0) ;
      kk = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 0);
  elseif (U10 > 0 & V10 < 0);
      kk = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 360);
      end
end 

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David Hill 2020-3-29

You should look at the atan2() or atan2d() functions.

Lilya 2020-3-29

Will check them, thanks a lot

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Answer 1

Daemonic 2020-3-29

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Is the purpose of your loop to compare the values of V10 and U10 element-wise? If so, you would need to modify slightly:

if V10(i) > 0 %compares the i'th element of V10 to 0

Secondly is kk the vector you're trying to create? If so, you'd need to make a similar adjustment (also, with a small vector it doesn't matter so much, but for larger ones, you'll speed things up if you pre-populate kk). Example:

        kk = nan(size(U10)); %creates empty vector for kk
        for i = 1:length (U10); 
            if(V10(i) > 0) %compares the i'th element of V10 to 0  
                kk(i) = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 180);
            elseif (U10(i) < 0 & V10(i) < 0) ;
                kk(i) = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 0);
            elseif (U10(i) > 0 & V10(i) < 0);
                kk(i) = ((180 / pi) * atan(U10(:,i)/V10(:,i)) + 360);
            end
        end 