ufl team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/9/6 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.

Ok. I forgot I also do that in SFC now (in the upcoming UFL-based version).

Even better: Instant can check the signature string and take the
checksum of it if it doesn't meet certain requirements like being a
valid filename and shorter than some constant limit.

--
Martin