ufl team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sat, Sep 06, 2008 at 01:30:04PM +0200, Martin Sandve Alnæs wrote:
> 2008/9/6 Anders Logg <logg@xxxxxxxxx>:
> > On Sat, Sep 06, 2008 at 01:02:29PM +0200, Martin Sandve Alnæs wrote:
> >> 2008/9/6 Anders Logg <logg@xxxxxxxxx>:
> >> > On Fri, Sep 05, 2008 at 10:58:08AM +0200, UFL wrote:
> >> >> One or more new changesets pushed to the primary ufl repository.
> >> >> A short summary of the last three changesets is included below.
> >> >>
> >> >> changeset:   224:4df4ffa5de1be81ed07fdea22569beb39e2e75f0
> >> >> tag:         tip
> >> >> user:        "Martin Sandve Alnæs <martinal@xxxxxxxxx>"
> >> >> date:        Fri Sep 05 10:58:06 2008 +0200
> >> >> files:       ufl/form.py
> >> >> description:
> >> >> Added __hash__ to Form, and caching of hash, repr and str so they are only
> >> >> computed the first time str(form), repr(form) or hash(form) is called.
> >> >
> >> > Very nice. I have the same thing in FFC (JITObject) which wraps a form
> >> > and remembers the signature for later reuse.
> >> >
> >> > One thing is that JITObject also includes the compiler flags
> >> > (quadrature or tensor representation etc) in the signature. Would it
> >> > be possible to add a mechanism like this to a Form so that it would
> >> > already be included in the signature? It would amount to attaching
> >> > a signature (for something else like compiler flags) to a Form that
> >> > gets included in the signature for the Form itself.
> >> >
> >>
> >> Done.
> >
> > Nice!
> >
> >> I guess adding a variable "_metadata" to Form which
> >> UFL doesn't really care about doesn't hurt anyone.
> >> But I guess the __hash__ would need to include _metadata
> >> as well? What have you done about that?
> >
> > I just include str(_metadata) in the string that generates the
> > signature. Here's the code for signature() in JITObject:
> >
> >    def signature(self):
> >        "Return signature"
> >
> >        # Check if we have computed the signature before
> >        if not self._signature is None:
> >            return self._signature
> >
> >        # Compute signature
> >        self.form_data = analyze.analyze(algebra.Form(self.form), simplify_form=False)
> >        form_signature = str(self.form)
> >        element_signature = ";".join([element.signature() for element in self.form_data.elements])
> >        options_signature = str(self.options)
> >        s = ";".join([form_signature, element_signature, options_signature])
> >        self._signature = "form_" + sha1(s).hexdigest()
> >
> >        return self._signature
> >
> 
> Two questions.
> 
> Why all the analysis? Isn't the "original" state of the form enough?
> With UFL I'd probably just do repr(form) + str(_metadata).
> But maybe there are some transformations that makes
> the comparison more robust, e.g. renumbering of objects
> like Function and BasisFunction.

I need to extract the elements for inclusion in the signature and they
are not available in str(form). It could be added to a .signature()
function in the form objects.

> You're using a checksum as the returned signature.
> Why not just return s?

It's too long and it won't work as a class name or file name. FFC uses
the signature as the name of the ufc:: classes it generates.

> Currently, Instant computes its own checksum of the given signature,
> which it uses for the module name in the disk cache.
> Either we can require the signature given to Instant to be
> a checksum already (or at least a valid part of a filename),
> and skip the checksum computation in Instant, or you can
> drop this checksum computation and just pass s to Instant.

That would be good. I'd prefer that Instant assumed it gets a hash
since FFC needs to generate a name for the ufc:: classes.

-- 
Anders

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