How can i save several 2-dimension-Matrices in a 3-dimension-Matrix

I have a function "exsearch2": it gives me a 2-dimension matrix.

Now i want to save several of these 2-dimension-matrices in just one 3-dimension matrix. i did it this way (A, B and C are necessary for exsearch2):

for i=1:N
X(:,:,i)=exsearch2(A,B(i),C(i));
end

Number of columns is always the same, every time exsearch2 is executed. The Problem is: The number of lines is not always the same. I have no possibility to know the number of lines before i execute exsearch2. Matlab now tells me, that there is a subscripted assignment dimension mismatch and i can understand it. But what is the solution?

Example to understand: exsearch2 gives me for i=1 this matrix:

1 2
2 1

for i=2 it's this matrix:

2 3
1 2
1 3

What i want at the end is:

X(:,:,1) = 
1 2
2 1
0 0

X(:,:,2)=
2 3
1 2
1 3

Answer 1

[Stephen23]

Try this:

for k=1:N
    tmp = exsearch2(A,B(k),C(k));
    X(1:size(tmp,1),:,k) = tmp;
end

This works by simply allocating the output of exsearch to a temporary variable tmp, and then only allocating to X as many rows as this tmp has. Also note that I changed the loop variable from i to k, because i and j are already defined as the imaginary unit, and it is best to avoid using them as variable names.

To improve performance you should also consider preallocating the array X instead of expanding it on every iteration. One easy way is to loop in reverse order:

for k=N:-1:1

[Andreas Peter]

Thank you very much. Sometimes, the easiest ways are the best. My mind was on the wrong track, you helped it getting to the right one :-)