perform calculation using for loop

So I have to use a for loop because I'm a student and the teacher said so. I've been trying to figure this one out and I'm sure theres a simple solution but because we are using matlab there aren't a whole lot of tutorials on using for loops when array operations are so much better.

I need to calculate the specific humidity using a for loop.

The equation is: q = (E*e)/P

where E = 0.622, e is a 96x144 matrix and, P represents p1 in my code which is another 96x144 matrix

I've coded something but I feel like the for loop is too simple.

Also the for loop and array operation return different values...is this normal?

% use for loop to calculate specific humidity
for q = 1:numel(p1)
    q_for = (0.622.*e)./(p1(q));
end
% calculate specific humidity using array operations
q_array = (0.622.*e)./p1;

[Walter Roberson]

Your output in your for loop should probably be going into a variable indexed at something.

[Adam Kevin Francis Baker]

q_for is the variable and i'm not sure what you mean by indexed at something...I thought thats what p1(q) was doing.

Answer 1

[Adam Kevin Francis Baker]

Ok I had to do a double for loop to make it work because I was dealing with a matrix so I ended up writing this code to solve my problem:

for q = 1:length(p1)
    for p = 1:min(size(p1))
        q_for(p,q) = (0.622.*e(p,q))./(p1(p,q));
    end
end

The array operation was simple:

q_array = (e.*0.622)./p1;

Answer 2

[Adam Kevin Francis Baker]

This is what I did...

for q = 1:numel(p1)
    q_for(q) = (0.622.*e(q))./(p1(q));
end

and for the array operation

q_array = (e.*0.622)./p1;

[Adam Kevin Francis Baker]

Still not quite right...the for loop is producing a 1x13824 array instead of a 96x144 array.

[Walter Roberson]

That would have been okay under one of two circumstances:

1. You pre-initialized q_for to be size(p1); or
2. You reshaped vector q_for to be size(p1)