ufl team mailing list archive

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

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
>
> --
> Anders

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.

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

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.

--
Martin