Sorry for the continued barrage of silly questions. It's my day to go through
sage gotcha's I'd accumulated.
Why doesn't this next substitution result in 5/y?
sage: P.<x,y>=ZZ[]
sage: (x/y).subs({x:5}) # this should be 5/y
x/y
sage: {x:5}.has_key(FractionField(P).gen(0))
False
Ok, the last False gives me a clue (after looking at the source for subs).
So, it seems fair that the generators aren't shared between the poly ring and
it's fraction field.
sage: {x:5}.has_key(P.gen(0))
True
So, then I branch out a bit. Why does the following work as I think it
should? I was going to fix the bug in the above, but I can't figure out what
to fix because it works with the QQ ring.
sage: P.<x,y>=QQ[] # NOTE: QQ not ZZ
sage: (x/y).subs({x:5})
5/y
sage: {x:5}.has_key(FractionField(P).gen(0))
True
Would someone be willing to look at the subs code and cast a vote about what
precisely to fix?
--
Joel
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