Math Forum Discussions

Chuck37

Posts: 84
Registered: 2/23/10

Re: Confusing spmd error
Posted: Jan 9, 2013 9:59 AM

Plain Text

Thanks, I'll give these idea a shot. It'll take a little doing since things are actually a little more complex than the example below.

From my print statement debugging so far, it appears that inside the function a structure is copied and somehow some of the values simply don't copy and have NaNs in their place. This is only the case inside spmd. I'll post back if I figure something out.

Edric M Ellis <eellis@mathworks.com> wrote in message <ytw6236zq03.fsf@uk-eellis0l.dhcp.mathworks.com>...
> "Chuck37 " <chuck3737@yahooremovethis.com> writes:
>
> > I have a function that is giving me an error when called within spmd
> > but I can't repeat it outside. e.g:
> >
> > x = <something>;
> > spmd
> > if labindex == 1
> > y = <something>
> > z = function(x,y);
> > end
> > end
> >
> > Gives me an error inside the function, but when I try to debug like this:
> >
> > z = function(x,y{1})
> >
> > It runs through just fine. This makes debugging very difficult.
> > Anyone have any idea of what would cause it not to run exactly the
> > same way in each case?
> >
> > The error is nothing parallel related by the way, it's actually a
> > singular matrix warning.
>
> Hmm, that's very strange. Do you still get the warning if you simply do
>
> x = <something>;
> y = <something>;
> z = function(x,y);
>
> How about if you do
>
> matlabpool open 1
> spmd
> x = <something>;
> y = <something>;
> z = function(x,y);
> end
>
> matlabpool close
> spmd
> x = <something>;
> y = <something>;
> z = function(x,y);
> end
>
> One other thing that has an outside chance of making a difference is
> that matlabpool workers are run in single computational thread mode,
> which means some algorithms will work slightly differently. You could
> try launching your desktop matlab with the "-singleCompThread" switch to
> see if that makes any difference.
>
> Cheers,
>
> Edric.