Problems with Conditionally execute statements

Hi, I'm having problems using if, elseif, and else. I'm trying to execute the statements for a matrix of satelite wind data... I pass from cartesian to polar coordinates and then from radians (on angle theta, the direction of the wind vector) to degrees, and I realized that matlab points the zero towards east in the rose (compass function). I want to make a conversion so that a theta angle of zero (or 360) points north, and 90 ° points east. I wrote this lines of code to do that... the weird thing is that the conditionall statements work when I use single values of theta, but when I run it for the whole matrix, it doesn't work, and it uses THE LAST (ELSE) statement, instead of my ELSEIF.. Any help with that? or any other way to make the conversion that I'm trying to do? Any matlab function to do it? Thanks a lot!

if tm < 0
tm = abs(tm)+90;
elseif tm > 90
tm=360+90-(tm); 
else 
 tm=abs(tm-90);   
end

 My data matrix (tm, already in degrees):

tm = [-159.3884 -173.0609 -174.9012 -178.0744  164.3687 -179.7163       NaN       NaN       NaN
   -161.7762 -179.5870  173.2305  176.2090  158.6573  177.0568       NaN       NaN       NaN
   -163.5107 -174.3112  165.9708  169.3241  152.4023  169.0777       NaN       NaN       NaN
   -170.2709  174.9133  178.0332  169.5016  150.9017  169.8905       NaN       NaN       NaN
    179.7075  174.8766  168.3010  150.7951  143.1325       NaN       NaN       NaN       NaN
    165.8388  165.0565  162.8236  140.7707       NaN       NaN       NaN       NaN       NaN
    152.2543  147.3183 -169.1261       NaN       NaN       NaN       NaN       NaN       NaN
    133.4060  131.5305       NaN       NaN       NaN       NaN       NaN       NaN       NaN]

[Azzi Abdelmalek]

your vector tm contains many values, what do you mean by

if tm<0

do you mean all values<0?

[Millo Marin]

Yes, because for some reason (which I don't know) matlab gives negative degrees in angles that are > 180°, and positive in angles < 180°. Thank you for your reply!

Answer 1

[Matt Fig]

If statements do not pick out elements of arrays!

 for ii=1:numel(tm)
    if tm(ii) < 0  % Need to look at each element one-at-a-time!
      tm(ii) = 90-tm(ii); 
    elseif tm(ii) > 90
      tm(ii) = 450-(tm(ii));
    else
      tm(ii) = abs(tm(ii)-90);
    end
 end

I encourage you to read that article by Loren, and click on the comments she refers to in the first sentence.

[Millo Marin]

Thanks a lot, it worked perfectly! Again, thanks for take the time to help.

Answer 2

[Azzi Abdelmalek]

% maybe is that what you need

 for k=1:length(tm)
    if tm(k)< 0
      tm(k) = abs(tm(k))+90; 
    elseif tm(k) > 90
      tm(k)=360+90-tm(k);
    else
      tm(k)=abs(tm(k)-90);
    end
 end

[Millo Marin]

That was the idea, except that length function gives you the number or columns in a matrix, and I needed to loop for each of the values in the matrix. Thank you for your reply!