create a vector and vector of matrix

[James Sherman Jr.]

I'm not exactly sure what you're aiming for, but for example
> repmat(0, length(A), 1)
could also be written as
> zeros(length(A), 1)

or
> repmat(1, length(A1), 1)
could be written as
> ones(length(A1), 1)

Doesn't work for twos though. :(  So for twos you could do:
> 2*ones(length(A2), 1)
but that would be somewhat inefficient compared to repmat if you're doing
lots of them.

To access a matrix using indices, there are two ways that I can think of.
First, you could use a cell array:
> C = cell(5,1);
> C{1} = A0;
> C{2} = A1;
and so on.  Then you access the A0 array by using C{1}  (note the curly
brackets, they denote that C is a cell array vs. a normal array).

The other way is to make a 3 dimensional array.  This would only work if all
the Ai matrices are of the same size.  Then you could do:
> C = zeros(size(A0, 1), size(A0, 2), 5);
> C(:, :, 1) = A0;
> C(:, :, 2) = A1;
Then you can access the A0 matrix by similarly using C(:, :, 1).  Note that
depending on what you're doing with the matrix (if you're multiplying the
matrices for example), you'll need to use the squeeze function on the matrix
since its technically still a 3d matrix even though the last dimension is 1.

Hope this helps.

On Wed, May 13, 2009 at 10:46 AM, Carlo Rossi <serosole at yahoo.it> wrote:

> Hello,
>  I need to create a vector; this work but is there something more compact?
>
> repmat(0, length(A), 1)
>
> eg:
> 0
> 0
> 0
> 0
> furthermore as I have to repeat the operation for 5 times, there is the way
> to do it in a loop as well:
> repmat(0, length(A0), 1)
> repmat(1, length(A1), 1)
> repmat(2, length(A2), 1)
> repmat(3, length(A3), 1)
>
> I mean: is it possible to create a vector of matrix indexes a vecot like
> this
> V = [A0 A1 A2 A3] and use V[i] to access to a matrix?
>
> thanks
>
>
>
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