Re: Iterative summation using sum(), fails with ezmesh

[Erik Leunissen]

On 04/11/2014 04:16 AM, Jordi Gutiérrez Hermoso wrote:
> On Thu, 2014-04-10 at 22:54 +0200, Erik Leunissen wrote:
>
> >                    4
> >                   __
> >     C(x,t) = 2*x* \  - exp(x+(i-0.5))^2
> >                   /   -----------------
> >                   --        t
> >                  i=-4
> >
> > Of course I'd prefer a vectorized way,
>
> I assume the negative goes inside the exp, not outside, as that is
> what you had in your code earlier.
>
> That being said, I can see a couple of ways. I have not timed either
> of them. Take your pick. There's a very straightforward way with
> arrayfun and a less transparent way using permute and exploiting
> broadcasting:
>
>      function z = C (xx, tt)
>        z = arrayfun ( @(x, t) 2*x*sum (exp ( -(x + (-4:4) - 0.5).^2))/t,
>                      xx, tt)
>        z = 2*xx.*sum (exp ( -(xx + permute (-4:4, [1,3,2]) - 0.5).^2), 3)./tt
>      endfunction

Aha, OK.

Thanks very much,

Erik Leunissen.

> HTH,
> - Jordi G. H.