how to have the final vector?

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 

[David Hill]

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

[Lilya]

Will check them, thanks a lot

Answer 1

[Daemonic]

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 

Sorry if I misunderstan your question...

[Lilya]

Thank you very much!!

Answer 2

[Ameer Hamza]

Use atan2, it takes care of the quadrants

result = atan2(U10, V10)

[Lilya]

much appreciated, will look at that now