How to store a matrix, A, in variable X, where X is also carrying a counter "i"

I have a matrix A, which I want to store in a varaible X.

Now I can do,

X=A;

But the varaible is X is having a counter i, beacuse the value of X variable in one iteration will be used in the next iteration and so on.

So, it put a counter like this;

X(i)=A;

But, in the above line, the indices error - Unable to perform assignment because the indices on the left side are not compatible with the size of the right side - is shown.

What should be the correct syntax, plaease tell me.

Answer 1

[Ulli Srinivasu]

Hi Neeraj,

simply create a structure.

X = struct();

X(i).A = A;

[Neeraj Kumar]

Hi Ulli Srinivasu,

What you said worked. But, now the variable X becomes 'struct", so I can't use it in further equations invloving multiplication of variable X.

Please, see the code from line 27 and the error in command window, in the pic attached below-

[Ulli Srinivasu]

use x(j-1).A, x(j).A, x(j+1).A

[Neeraj Kumar]

It worked!! Thanks Ulii Srinivasu!!

Answer 2

[Sindar]

Simple way: add a third dimension, "pages":

X(:,:,i) = A;

But, if you only need the last iteration, it's better to store just the current and last iteration. Something like:

n=10;
m=4;
X_new = rand(n,m);
for ind=1:10
    X_old = X_new;
    X_new = X_old.^2;
end

[Neeraj Kumar]

I tried the solution you provided-

X(:,:,i) = A;

Say, matrix,

A=[2; 2; 2]

and, i=2, what MATLAB does is, it creates two matrices, shown below, in the result-

x(:,:,1) =

     0
     0
     0

x(:,:,2) =

     2
     2
     2

So, actually i wanted just the second matrix, but it creates one extra matrix (the null matrix) which is undesired and makes the results faulty.

If i=3, it will be create two extra matrices (null matrices). In my program, i is varying upto i=25, so there it will create 24 extra matrices.

So, what should be done now?

[Neeraj Kumar]

Sindar??

[Walter Roberson]

What you are seeing displayed is not two matrices, it is a way to represent a multidimensional matrix of numeric values on the command window.

I would suggest that you use SIndar's X_old strategy.

[Neeraj Kumar]

Ok, i will try this X_old strategy. Thanks Walter! Thanks Sindar!