MATLAB: expressing a double index equation as a matrix

[Deathcrush]

Just an urgent doubt, I am new to matlab.

So imagine an equation that has two indexes, and that can be expressed as a matrix, how can I do something like this in Matlab? using a for cycle?

 

[Mark44]

Can you give us an example? What you've said is on the vague side.

 

[Deathcrush]

like for example, if I have I_ij=v_i/v_j considering that I know v for every i or j

 

[Grep]

Just an urgent doubt, I am new to matlab.

So imagine an equation that has two indexes, and that can be expressed as a matrix, how can I do something like this in Matlab? using a for cycle?

Often unnecessary to use a for loop, but you can always do things like this:

a = [1 2 3; 4 5 6; 7 8 9];
for i = 1:3,
    for j = 1:3,
        a(i,j)
    end
end

Matrices is pretty much what MATLAB is all about. Probably, all your beginner questions can be found in various MATLAB documentation. I'd suggest finding it and reading it.

 

[Deathcrush]

well, the problem is that my equation is not so simple, it is actually a pretty big fluid dynamics model for calculating the viscosity of a mixture of 10 gases, so I have an equation, lots of constant properties, and I am trying to get a 10x10 matrix :S

 

[Grep]

like for example, if I have I_ij=v_i/v_j considering that I know v for every i or j

I'm rusty on my MATLAB, but something like this perhaps?

for i = 1:length(v),
    for j = 1:length(v),
        r(i,j) = v(i)/v(j);
    end
end
r

Note that division by zero will happen if there's a single 0 in there...

 

[Deathcrush]

oh thanks a lot Grep, that REALLY helped me, now I've finished :)