Re: Vectorization

[Bård Skaflestad]

On Tue, 2014-10-07 at 21:12 -0700, Thomas D. Dean wrote:
> I have data collected from an optical encoder attached to a DC motor. 
> The motor is driver with a PWM signal.
> 
> PWM = [0:20:240 255 240: -20:-240 -255 -240:20:0]
> 
>  > size(encoder)
> 20571 1
> 
> I want mean(encoder(PWM==20)) for each of the PWM values.

Here's one *possible* option.  I'm not going to claim it's particularly
good because it generates an intermediate DOUBLE matrix of size

    NUMEL(UNIQUE(pvals))-by-NUMEL(encoder)

so you may want to look into a solution based on ACCUMARRAY or SPARSE
instead--especially if memory is tight.

        [up, iu, iu] = unique(pvals(:));
        v = double(up == reshape(pvals, 1, [])) ...
            * [ encoder(:), ones([numel(encoder), 1]) ];
        L = v(:,1) ./ v(:,2);
        L = reshape(L(iu), size(pvals));


Sincerely,
-- 
Bård Skaflestad <address@hidden>
SINTEF ICT, Applied Mathematics