Hello all,
I am developing patch # 15780. We want to use fast_callable to increase the
speed.
The changes we have work for most cases. However, when we try to evaluate the
expression tree built for a polynomial ring over a PowerSeriesRing, an
exception is thrown.
T.<z>=PowerSeriesRing(ZZ)
P.<x,y>=PolynomialRing(T)
f=x^2+x*y
g=fast_callable(f)
g(1,1)
The cause is in generic_power_c() in sage/structure/element.pyx. Basically, the
PowerSeriesRing element 1 fails to be recognized as the integer 1 causing the
exception to be thrown.
try:
from sage.rings.integer import Integer
n = int(Integer(nn))
except TypeError:
raise NotImplementedError, "non-integral exponents not supported"
This is occuring because the expression from fast_callable has a term ('ipow',
n) where n is actually an integer, but whose parent is the coefficient ring of
the polynomial ring.
The question here is basically: what part of this needs to be fixed? It seems
odd that the exponents being returned from fast_callable are in the base ring
causing the call to generic_power. This expression should be fast to evaluate
and, even if it worked, this is certainly slowing it down. But it also is odd
that Integer() is unable to coerce a power series integer.
Dillon Rose
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