Re: Testing for function handles

[Richard]

On 09/11/2011 10:32, Juan Pablo Carbajal wrote:
> On Wed, Nov 9, 2011 at 11:01 AM, Richard<address@hidden>  wrote:
> > On 09/11/2011 08:18, Dr. Alexander Klein wrote:
> > > Good morning,
> > >
> > > is there any preferred way to check whether a given parameter or variable
> > > contains a function handle?
> > >
> > > I find myself strcmp'ing the result of typeinfo quite often, but this is
> > > really clumsy. Then again, ishandle only checks for graphics handles ...
> > >
> > > Best regards,
> > >
> > >         Alex
> > if it is octave code you can use the 'isa' function e.g.
> >
> > isa(@sin, 'function_handle')
> >
> > but maybe I'm misunderstanding and you mean in the C++ sources or something.
> >
> > Richard
> >
> > --
> > The University of Edinburgh is a charitable body, registered in
> > Scotland, with registration number SC005336.
> Checking
> f = @(x)x;
> n=5e4;
> t0=cputime;
> for i=1:n
>    strcmp(typeinfo(f),'function_handle');
> end
> t=cputime-t0
>
> t0=cputime;
> for i=1:n
>    isa(f,'function_handle');
> end
> t=cputime-t0
>
> I get
> t =  1.0521
> for strcmp
> t =  5.0083
> for isa
>
> Is the benchmark correct?

Yes, well on my machine:

f = @(x)x;
n=5e4;
tic;
for i=1:n
  strcmp(typeinfo(f),'function_handle');
end
toc

tic;
for i=1:n
  isa(f,'function_handle');
end
toc

Yields

Elapsed time is 0.862049 seconds.
Elapsed time is 3.15218 seconds.
octave-3.2.4.exe:3>

Although as you can see I'm using an out of date version of Octave

Not sure why this should be so though, but maybe this is why isa is so 
sparsely documented?


--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.