On Mar 31, 5:14 pm, "john.hoebing" <jlhs...@gmail.com> wrote:
> sage: a=diff(f,x,x)+diff(f,x)/x
> sage: str(a)
> 'D[0](f)(x, y)/x + D[0, 0](f)(x, y)'
If I understand correctly, you would like to be able to put the above
string into sage and get the expression back? That is of course a very
reasonable goal. The class FDerivativeOperator can be used to create
the appropriate expressions, but suffers from the fact it uses a
different syntax. We need to build a wrapper that does allow the
indexing syntax above. Something along these lines would do the trick:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
from sage.symbolic.operators import FDerivativeOperator
class Doperator:
def __init__(self,vars=None):
self.vars= [] if vars is None else vars
def __call__(self,f):
return FDerivativeOperator(f,self.vars)
def __getitem__(self,i):
if isinstance(i,tuple):
newvars=self.vars+list(i)
else:
newvars=self.vars+[i]
return Doperator(newvars)
D=Doperator()
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
With that code in place we can indeed do:
sage: var('x,y')
sage: D[0](f)(x, y)/x + D[0, 1](f)(x, y)
D[0](f)(x, y)/x + D[0, 1](f)(x, y)
Perhaps this should go into the library somewhere. I'm not sure we can
afford to predefine D like this, given it's such a commonly used
symbol. Maple does it, though.
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