How can I index a matrix with only one number in Matlab inside a loop?

Hello!

I'm new in the forum and I would like a little help... I'm facing the following problem: I have a loop variable k that goes from 1 to 12, and in each step k it has associated with it a matrix.

I would like to do something like this: x(1) = Matrix1, ...,x(k) = Matrixk, but I can't...Matlab says "??? In an assignment A(I) = B, the number of elements in B and I must be the same."

Each k has a 19x73 matrix associated, so it will be useful to find a way to do this indexing...haha, meanwhile the program has 12 blocks just for do this job... Any help is appreciated. Thanks!

[Kishor]

give example clearly.Check out what is cell array. use it

Answer 1

[Fangjun Jiang]

Use n-D array or cell array

%n-D array
x=zeros(12,19,73)
for k=1:12
x(k,:,:)=rand(19,73);
end

% cell array
x=cell(12,1);
for k=1:12
x{k}=rand(19,73);
end

[Jan]

+1: A complete answer for a standard problem.

Answer 2

[Andre L]

Fangjun, Thanks! I really appreciate your reply and I think it will work in my problem. But I never used more than 2 indices in Matlab...and this is the problem with your solution...i've tried in almost any ways to implement it in my program, but none of these works.

This is what I want to do in the program:

http://imageshack.us/f/199/matlabs.jpg/

After the i-j loop, in the k-th step, a 19x73 matrix should be associated whith this k, but the output is always the last k only. Am I indexing correcly, with (i,j) or it should be (k,i,j) ?

[Fangjun Jiang]

Your code is not executable with missing variables. You can just copy and paste all your code here. Remember to apply the {}code format to it.

Answer 3

[Andre L]

Hello! This is my code:

function x = irrad_anual_total;

clc

[H_betam,Kt,Kd,H_mensal,Hd_mensal,H_0,lat,delta,dia,ang_hor] = irrad_incl;
ang_hor = 0; 
refl = 0.2;

for k = 1:12

      costetaZS(k) = sind(delta(k))*sind(lat)+cosd(delta(k))*cosd(lat)*cosd(ang_hor);
      B_0(k) = 1000*(H_mensal(k)-Hd_mensal(k));
      B(k) = B_0(k)/costetaZS(k);

      for i = 1:19

          for j = 1:73

          beta = 5*i-5;  
          azim = -185+5*j; 

          costetaS(k) = sind(delta(k))*sind(lat)*cosd(beta)-...                  sind(delta(k))*cosd(lat)*sind(beta)*cosd(azim)+cosd(delta(k))... *cosd(lat)*cosd(beta)*cosd(ang_hor)+cosd(delta(k))*sind(lat)...
*sind(beta)*cosd(azim)*cosd(ang_hor)+cosd(delta(k))*...
sind(azim)*sind(ang_hor)*sind(beta);

          Bdir(i,j) = B(k)*max(0,costetaS(k));

          Ddif(i,j) = 1000*0.5*Hd_mensal(k)*(1+cosd(beta));

          Ralb(i,j) = 1000*0.5*refl*H_mensal(k)*(1-cosd(beta));

          Total(i,j) = Bdir(i,j)+Ddif(i,j)+Ralb(i,j);

          end
      end
          T(k) = Total(i,j) %Don't worked
  end

.

My goal is to obtain the sum of the 12 matrices and get at the end a 19x73 matrix named Total.

Thanks again Fangjun for your reply!

[Fangjun Jiang]

Still not executable for others. We don't have irrad_incl.

Are you saying that you have 12 matrices, each is 19x73 and you want to add them together and get one 19x73 matrix? It doesn't sound like you need a 3-D matrix. You can always try on a small example to give you some ideas.

total=zeros(2,3)

for k=1:3

total=total+rand(2,3)

end

[Andre L]

I got it Fangjun!

What I did was to use the idea of cell array. At the code, I replaced the "T(k) = Total(i,j)" by "T{k} = Total", changing () to {}. In this way, each k at the end of the i-j loop was associated with its matrix, for example, T{11}. Really wasn't needed a 3-D matrix.

The sum is performed as T{1}+...+T{12} (as you can easily see, I am new in programming - by the way, in english too haha). In the end I got the result I needed, but if there are another way to perform this sum it would be great!

Thanks again. This was a important question...indeed I didn't find nothing in internet about indexing a matrix with an escalar like this.

[Fangjun Jiang]

Okay! If you just need the sum "T{1}+T{2}+...+T{12}", not the individual T{1}, T{2} to T{12}, you can utilize array to save memory.

Right before for k=1:12 line, add T=zeros(19,73)

Replace "T(k) = Total(i,j) %Don't worked" line with T=T+Total;

[Andre L]

Wow! It worked haha!

Thank you infinitely Fangjun!

This is a program to analyse the average solar radiation at any inclination and orientation relative to north-south. You just help to save the humanity with solar power man haha!

I will study the n-D array and cell array that you reply on the first time, I think it will be useful.

Thanks again.