dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Jul 16, 2009 at 08:26:21AM +0200, Benjamin Kehlet wrote:
> >> On Thu, Jul 09, 2009 at 08:20:54AM +0100, Garth N. Wells wrote:
> >>>
> >>>
> >>> Anders Logg wrote:
> >>> > On Thu, Jul 09, 2009 at 08:05:42AM +0100, Garth N. Wells wrote:
> >>> >>
> >>> >> Anders Logg wrote:
> >>> >>> On Thu, Jul 09, 2009 at 12:14:14AM +0200, DOLFIN wrote:
> >>> >>>> One or more new changesets pushed to the primary dolfin
> >>> repository.
> >>> >>>> A short summary of the last three changesets is included below.
> >>> >>>>
> >>> >>>> changeset:   6458:8dacb335c9825380a2e614f5de2ae89f79131995
> >>> >>>> tag:         tip
> >>> >>>> user:        "Garth N. Wells <gnw20@xxxxxxxxx>"
> >>> >>>> date:        Wed Jul 08 23:13:53 2009 +0100
> >>> >>>> files:       demo/ode/reaction/cpp/main.cpp
> >>> >>>> description:
> >>> >>>> Comment out reaction ODE demo. Gives error when run.
> >>> >>> What happens when you run it? Same as for the buildbot?
> >>> >>>
> >>> >>>   terminate called after throwing an instance of
> >>> 'std::runtime_error'
> >>> >>>   what():  *** Assertion (e1 != -1) [at
> >>> >>>   dolfin/ode/MultiAdaptiveTimeSlab.cpp:926 in cg_feval()]
> >>> >>>
> >>> >>> This does not happen for me. It works fine and it's not because I
> >>> >>> don't trigger assertions, I checked.
> >>> >>>
> >>> >>> Any special configuration you are using? I'm running without GMP.
> >>> >>>
> >>> >> It fails with GMP and works with GMP.
> >>> >
> >>>
> >>> I was a bit hasty - fails with GMP and works without GMP.
> >>>
> >>> Garth
> >>
> >> ok, most likely some floating-point comparison that fails.
> >>
> >> I'll ask Benjamin Kehlet to look at it or fix it myself later
> >> otherwise.
> >
> The problem is that in the reaction demo a number of real variables are
> declared in main before the ode object is created.The precision of these
> variables are incorrect since GMP hasn't been initialized at that time.
> We need to initialize precision in GMP by calling mpf_set_default_prec()
> before the first real is declared. We now do this in the constructor of
> class GMPObject which ODE inherits.
> The only way (I can think of) ensure absolutely, is to wrap class real and
> check in the constructor, but I guess the overhead by checking this every
> time a real is declared is unacceptable.
> Another suggestion is to do the initalization in a function
> dolfin::set_precision(uint prec) and force the user to call this function.
> We can check that this has been done when an ode object is created and
> otherwise give an error message. The documentation and error message must
> state clearly  that this must be done _before_ creating any real
> variables. The bad thing with such a solution is that the same user code
> will not run both with and without GMP enabled, since we force the user to
> call set_precision, which doesn't make sense when running with the normal
> (double) precision.
> Anders has suggested making this a parameter "floating-point precision" in
> Dolfin, but I can't see what should then trigger the call to
> mpf_set_default_prec() before any reals are declared.

Having a function named set_precision() sounds like the best solution.

We can let this function return a warning instead of an error if GMP
is not available. Then the demo would run both with and without GMP.
I imaging that set_precision() will only be used in one or two ODE
demos so it should be ok.

Would that work?

-- 
Anders

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