multiple if statements in matlab

   % inputs are a_s, p, t, a
   % a_s=single number
   % p,t,a are (nX1) column vectors each 
   % output is P (also a column vector of dimension (nX1))

   %---------actual equations--------
    if a_s<a<=a_s-180
            P=p+t     for p<=180-t
            P=p+t-180 for p>180-t
    if a<=a_s or a_s-180<a       
            P=p-t     for p>=t    
            P=p-t+180 for p<t
    Note: The two if's are connected.
   %---Matlab prog. for above eqn.---    
   if a_s<a<=a_s-180
     if p<=180-t    %------(1)
         P=p+t;
     elseif p>180-t %------(2)
         P=p+t-180;
     end
   elseif a<=a_s | a_s-180<a
     if p>=t        %------(3)
         P=p-t;
     elseif p<t     %------(4)
         P=p-t+180;
     end
   end
   % I couldn't figure the mistake. While running the program, (1)&(3) are
   % ignored in matlab.

[Image Analyst]

After you supply sample/typical values for a_x, p, t, and a, then I will run it. Off the top of my head it looks like this could be vectorized.

[Rakesh]

    Thanks for the reply. Here are few values of the variables:
    a=[10 11 55 22 25 34 39 40 41 52 54 76 113 125 133];
    p=[40 51 40 22 45 19 97 79 135 222 175 138 125 77 20]';     
    t=[80 75 45 71 71 63 61 72 89 78 73 54 9 54 65]';
    a_s=283;

[Jürgen]

as said above the code works fine , but see my answer: I still wonder what you want to do, you gave us a column vectors a, p and t so with those inputs and the provided code you can only run the program and see that none of your conditions are fullfilled, unless if you want to run it elementwise then you need to add a for loop for indexing, but in that case you can calculate it directly with the vector, e.g. by using the result of comparing a to a_s (zero and ones) to multiply with -t and +t

Answer 1

[Jürgen]

Hey, difficult to check it without example values but if I understand it well you are comparing a column vector p to a column t, so then all element needs to be larger or smaller than the ones in the other column no? or do you want to compare element wise

Answer 2

[Image Analyst]

How can this ever be true:

a_s< a <= a_s-180

A number can't be greater than a certain number and also less than the number, and certainly not less that that number minus 180!

[Jürgen]

okay should have noticed that :-)

[Matt Fig]

In MATLAB this statement could easily be true. For example:

>> a_s = 200;
>> a = 1;
>> a_s< a <= a_s-180

ans =

       1

[Jürgen]

Hey Matt, could you explain that please? I normally use: a_s< a& a <= a_s-180 and that gives as expected ans = 0 so they other statement acts as an "or" operator or what? regards,J

[Image Analyst]

Yes that's correct. We see this all the time, and know that often causes problems because that is not what the user was intending when he coded it up. Jurgen you should use && in that situation, because it's a boolean test, not a bit-by-bit operation that you want to do.

[Matt Fig]

MATLAB evaluates left to right. So as you wrote it, the expression evaluates this way

(a_s< a) <= a_s-180

What you probably meant was

a_s< a  &&  a<= a_s-180

But then IA's original comment applies.

[Jürgen]

ok thanks