Hi all, While playing with the quotient of a polynomial ring with an ideal, I encountered several glitches.
*) Trying to compute the inverse of something which is not invertible. I know it is kind of weird to try this. However, it raises a NotImplementedError exception, instead of something more informative such as NonInvertible or whatever. I am willing to patch this, but could someone tell me what is the correct exception to raise? *) Non-deterministic output of some (presumably deterministic) functions Here is an example : sage: R.<x1,x2> = QQ[] sage: I = R.ideal(x2**2 + x1 - 2, x1**2 - 1) sage: test = I.gen(0) + x2*I.gen(1) sage: (test).lift( I ) [1, x2] # this is correct sage: R.<x1,x2> = QQ[] sage: I = R.ideal(x2**2 + x1 - 2, x1**2 - 1) sage: test = I.gen(0) + x2*I.gen(1) sage: (test + 1).lift( I ) [0, 0] # this is correct sage: R.<x1,x2> = QQ[] sage: I = R.ideal(x2**2 + x1 - 2, x1**2 - 1) sage: test = I.gen(0) + x2*I.gen(1) sage: (test).lift( I ) [0, 0] # this is WRONG !!! should be [1, x2] It looks like this could be a caching issue, so I am not sure whether I need to open a new ticket for this, or if it is already "catch" by an already-opened ticket. *) Segfault The same kind of problem allows a small piece of code to cause segfaults in SAGE (apparently in singular-related stuff) : sage: R.<x1,x2> = QQ[] sage: S = R.quotient_ring( R.ideal(x2**2 + x1 - 2, x1**2 - 1) ) sage: 1 / S(x1 + x2) # should raise NotImplementedError sage: sage: R.<x1,x2> = QQ[] sage: S = R.quotient_ring( R.ideal(x2**2 + x1 - 2, x1**2 - 1) ) sage: S.is_integral_domain() ---> BOOM *) bizarre output of p.lift(….) When R is a Polynomial Ring, I is an ideal of R, and p is a polynomial of I, then p.lift( I ) returns a polynomial combination of a (groebner) basis of I which is equal to p. However, when p is not in I, then p.lift( I ) returns [0,0,…,0]. I find this a bit strange. Should p.lift(…) raise an exception instead? This would be a change of specification, so I guess it should be discussed first… --- Charles Bouillaguet http://www.lifl.fr/~bouillaguet/ -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
