Re: syntax help: simple formula expansion (sub-indexes with vectors)

[Paul Kienzle]

The simplest way is to do the elements separately:

        a = h/n * ([1:n]' + 0.5);
        d = [ I(1)+a*x(1), I(2)+a*x(2)];

If d were a k-vector rather than a 2-vector, then put it in a loop:

        d = zeros(n,k);
        for i=1:k, d(:,k) = I(k) + a*x(k); end

You can do it without the for-loop using:

        d = ones(n,1)*I + (a*ones(1,k)) .* (ones(n,1)*x);

but that increases memory usage, and may actually be slower.

Paul Kienzle
address@hidden

On Jun 3, 2004, at 11:46 AM, edA-qa mort-ora-y wrote:

> Although I've been working with octave for a little while now I am 
> still having a lot of problems working with the most basic 
> expressions.  Can somebody please indicate to me the prefered way to 
> handle the below example.
>
> Given these variables (not in octave notation to avoid confusion):
>         l is a 2-space vector (ex. (4,5), in octave: [4,5])
>         x is a 2-space vector
>         h is a real number
>         n is an integer
>         i is the range of numbers [1,n]
>
> I want to evalute the following function for every integer in i:
>
>         d(i) = l + ( h/n * ( i + 0.5 ) ) * x
>         
> I want to create the variable d that has the result of the function 
> for each element of i.  I try doing something like below, but I keep 
> getting errors.
>
>         l=[1,1];
>         x=[0,1];
>         h=6;
>         n=3;
>         i=1:n
>         for q=i; d(q)=l-((h/n)*(q+0.5))*x; end
>
>         error: A(I) = X: X must be a scalar or a vector with same length as I
>
> How do I do this? (If possible it'd be nice not to use a loop, but 
> since I can't even get the loop working I feel unqualified to find a 
> better solution)
>
> --
> edA-qa mort-ora-y
> Idea Architect
> http://disemia.com/
>
>
>
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