Bugs item #904543, was opened at 20040225 13:57
Message generated for change (Settings changed) made by robert_dodier
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>Category: Lisp Core  Taylor
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Stavros Macrakis (macrakis)
Assigned to: Nobody/Anonymous (nobody)
Summary: ratcoeff incompatible with taylor [x,y]
Initial Comment:
t: taylor(sin(x+y),[x,y],0,5)
=> y+x....
ratcoeff(t,x,1) => 0+...
but
ratcoeff(ratdisrep(t),x,1) => (y^412*y^2+24)/24
The ratdisrep case should be taken as the definition. If
we don't want to do that, it should at least give an
error, saying that it doesn't handle multivariate series.
It would be nicer, though, if ratcoeff took multiple
arguments, e.g.
ratcoeff(t,x,1,y,0)
==
ratcoeff(ratcoeff(t,x,1),y,0)
=> x+y
ratcoeff(t,[x,y],1) => x+y
ratcoeff(t,[x,y],2) => 0
ratcoeff(t,[x,y],3) =>
(y^3+3*x*y^2+3*x^2*y+x^3)/6
but that's another matter....

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