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Weird behavior BuiltinFunction

asked 2012-10-05 00:22:43 -0500

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Dear Sage,

I'm trying to program qPochhammer functions which can interact with sage in a nice way. However I encounter some weird behavior of these new BuiltinFunctions. This is what I made: from sage.symbolic.function import BuiltinFunction

class qPochhammer(BuiltinFunction):

    def __init__(self, m=1, expand_exp=False):
        self.m = m
        self.expand_exp = expand_exp
        self.has_arguments = False

        BuiltinFunction.__init__(self, 'qPochhammer(%i)' % self.m, nargs=(m+2))

    def _latex_(self):
        if self.has_arguments:
            return '(%s; %s)_{%s}' % (self.a, self.q, self.n)
        return 'qPochhammer'

    def _qPochhammer1(self, a, q, n):
        if n == 0:
            return 1
        return (1 - a*q**(n-1))*self._qPochhammer1(a, q, n-1)

    def _expand(self):
        return prod([self._qPochhammer1(elm, self.q, self.n) \
                     for elm in self.a])

    def _eval_(self, *args):
        if len(args) != self.m + 2:
            raise RuntimeError, args

        if self.expand_exp:
            return self.evaluate(args[:self.m], args[-2], args[-1])

        return None

    def _evalf_(self, *args, **kwds):
        if type(self.a) == tuple:
            return self._expand()
        return self._qPochhammer1(self.a, self.q, self.n)

    def evaluate(self, a, q, n):
        self.a = a
        self.q = q
        self.n = n

        self.has_arguments = True

        if type(self.a) == tuple:
            return self._expand()
        return self._qPochhammer1(self.a, self.q, self.n)

Now I try the following the the sage console:

sage: a, b, c, q = var('a b c q')
sage: qshift3 = qPochhammer(m=3, expand_exp=True)
sage: qshift3(a, b, c, q, 2)
(c - 1)*(b - 1)*(a - 1)*(c*q - 1)*(b*q - 1)*(a*q - 1)
sage: qshift2 = qPochhammer(m=2, expand_exp=True)
sage: qshift2(a, b, q, 2)
RuntimeError                              Traceback (most recent call last)

/home/noud/work/sage/local/lib/python2.7/site-packages/sage/all_cmdline.pyc in  <module>()
----> 1 

/home/noud/work/sage/local/lib/python2.7/site-packages/sage/symbolic/ in sage.symbolic.function.Function.__call__ (sage/symbolic/function.cpp:4941)()
--> 432 

/home/noud/work/sage/local/lib/python2.7/site-packages/sage/all_cmdline.pyc in _eval_(self, *args)
---> 29 

RuntimeError: (a, b, q, 2)

Can someone explain to my why I get a RuntimeError and how to solve this?

Best regards, Noud

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1 answer

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answered 2012-10-08 05:41:49 -0500

Some debug output after the lines pasted in the question:

sage: %debug                                     
> /home/burcin/sage/
     27         if len(args) != self.m + 2:
---> 28             raise RuntimeError, args

ipdb> print self

Note that the function in use is not qPochhammer(3). ATM, we expect each BuiltinFunction to be instantiated once. In other words, each class corresponds to exactly one symbolic function. This is evident in the check on line 827 of sage/symbolic/function.pyx. Changing this to also check for the name of the function fixes your problem.

Patch waiting for review on trac ticket #13586.

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Nice! Thank you for this fix!

Noud gravatar imageNoud ( 2012-10-10 01:20:46 -0500 )edit

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Asked: 2012-10-05 00:22:43 -0500

Seen: 125 times

Last updated: Oct 08 '12