The behavior is quite erratic; my first example was more complicated; I
eliminate terms and sometimes it worked, some times not.
El domingo, 4 de agosto de 2019, 15:19:59 (UTC+2), vdelecroix escribió:
>
> I confirm the bug on 8.9.beta5. It is most probably a bug in Pynac. Note
> that if you multiply by 2 it "works"
>
> sage: (2*num).factor()
> (16*r^6 - 32*r^4*x^2 + 16*r^2*x^4 + 32*r^4*y^2 + 32*r^2*x^2*y^2 +
> 16*r^2*y^4 + 80*r^2*x^2 + 16*x^4 + 16*r^2*y^2 + 32*x^2*y^2 + 16*y^4 -
> 16*x^2 - 16*y^2)*r^4/(r^6 + 6*r^4*x^2 + r^2*x^4 + 2*r^4*y^2 +
> 2*r^2*x^2*y^2 + r^2*y^4 - 2*r^2*x^2 + x^4 + 2*r^2*y^2 + 2*x^2*y^2 + y^4)^2
>
>
> Le 24/07/2019 à 13:31, Enrique Artal a écrit :
> > I have encountered a problem with factor in SR which can be avoided but
> it
> > shows a problem. If I run this code:
> >
> > var('t',domain='complex')
> > var('r,x,y',domain='real')
> > h= r^6+r^4*t^2 + 4*r^4*t*conjugate(t) + r^4*conjugate(t)^2 +
> > r^2*t^2*conjugate(t)^2 - r^2*t^2 - r^2*conjugate(t)^2 +
> t^2*conjugate(t)^2
> > H=h(t=x+I*y).factor()
> >
> num=1/2*(H.derivative(x)/H).derivative(x)+1/2*(H.derivative(y)/H).derivative(y)
>
>
> > num.factor()
> >
> > I get the following error
> >
> >
> ---------------------------------------------------------------------------ValueError
>
> Traceback (most recent call
> last)<ipython-input-1-bfb20671ab22> in <module>() 6
> H=h(t=x+I*y).factor() 7
> num=Integer(1)/Integer(2)*(H.derivative(x)/H).derivative(x)+Integer(1)/Integer(2)*(H.derivative(y)/H).derivative(y)---->
>
> 8 num.factor()
> >
> /home/artal/sage/local/lib/python2.7/site-packages/sage/symbolic/expression.pyx
>
> in sage.symbolic.expression.Expression.factor
> (build/cythonized/sage/symbolic/expression.cpp:57759)() 11107 cdef
> GEx x 11108 cdef bint b> 11109 if dontfactor or not
> self.is_rational_expression(): 11110 m = self._maxima_()
> 11111 name = m.name()
> >
> /home/artal/sage/local/lib/python2.7/site-packages/sage/symbolic/expression.pyx
>
> in sage.symbolic.expression.Expression.is_rational_expression
> (build/cythonized/sage/symbolic/expression.cpp:15368)() 2030
> False 2031 """-> 2032 return all(part.is_polynomial(v)
> 2033 for part in (self.numerator(), self.denominator())
> 2034 for v in part.variables())
> >
> /home/artal/sage/local/lib/python2.7/site-packages/sage/symbolic/expression.pyx
>
> in genexpr (build/cythonized/sage/symbolic/expression.cpp:15110)() 2031
> """ 2032 return all(part.is_polynomial(v)-> 2033
> for part in (self.numerator(), self.denominator()) 2034
> for v in part.variables()) 2035
> >
> /home/artal/sage/local/lib/python2.7/site-packages/sage/symbolic/expression.pyx
>
> in sage.symbolic.expression.Expression.numerator
> (build/cythonized/sage/symbolic/expression.cpp:48252)() 9377
> sig_on() 9378 try:-> 9379 ex =
> self._gobj.numer() 9380 finally: 9381
> sig_off()
> > ValueError: divide: arguments must be polynomials over the rationals
> >
> >
> > This error does not happen if I erase some terms of h; and some times it
> gives the error only if I did not restart the jupyter notebook. Any ideas?
> Enrique.
> >
>
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