Re: Apply Polyval to Array

[Thomas D. Dean]

On 06/12/2016 08:42 PM, Dmitri A. Sergatskov wrote:
> On Sun, Jun 12, 2016 at 10:25 PM, Doug Stewart <address@hidden
> <mailto:address@hidden>> wrote:
>
>
>
>     On Sun, Jun 12, 2016 at 10:03 PM, Thomas D. Dean
>     <address@hidden <mailto:address@hidden>> wrote:
>
>         I want to vectorize this:
>
>         p1 = [1,2,3;4,5,6;7,8,9];
>         for idx=1:3
>            polyval(p1(idx,:),0)
>         endfor
>
>         cellfun("polyval",{p1},{[0;0;0]}); ## fails
>         arrayfun("polyval",p1,0 "UniformOutput",false)); ## wrong
>         arrayfun("polyval",p1,zeros(3,3), "UniformOutput",false); ## wrong
>
>         Tom Dean
>
>         _______________________________________________
>         Help-octave mailing list
>         address@hidden <mailto:address@hidden>
>         https://lists.gnu.org/mailman/listinfo/help-octave
>
>
>     does this help
>
>     p1 = [1,2,3;4,5,6;7,8,9];
>     t=[1 2 3]
>     f=@(t) polyval(p1(t,:),0)
>     arrayfun(f,t)
>
>
>
> ​it works, but hardly faster than the loop on my computer.
>
> ​>> p1=rand(1000);
>  >> tic; for idx=1:1000; polyval(p1(idx,:),0) ; endfor; toc
> Elapsed time is 4.96287 seconds.
>  >> t=1:1000;
>  >> f=@(t) polyval(p1(t,:),0)
> f =
>
> @(t) polyval (p1 (t, :), 0)
>
>  >> tic; arrayfun(f,t); toc
> Elapsed time is 4.82834 seconds.
>
> ​Dmitri.
> --

To get faster, the interpreter can not be involved in a loop, as in the 
case of the function t.

Tom Dean