#1163: assume seems to have some undesired side-effects
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Reporter: zimmerma | Owner: gfurnish
Type: defect | Status: assigned
Priority: major | Milestone: sage-4.1.2
Component: calculus | Keywords:
Reviewer: | Author:
Merged: |
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Comment(by kcrisman):
A very interesting exchange on the Maxima list indicates that Maxima isn't
so much at fault as Sage's use of it, even in the sketchy-looking cases.
This is Robert Dodier's response:
{{{
Well, it's true that assume isn't very strong, but at least Maxima
seems to be able to figure out these examples.
What you want is equal(x, z) instead of x = z.
"=" is essentially identity (i.e. are the left and right-hand sides
the same expression), while equal is equivalence (equal value).
Likewise the distinction between "#" and notequal.
Here's what I get with Maxima 5.19.2.
(%i2) assume(x>=y,y>=z,z>=x);
(%o2) [x >= y, y >= z, z >= x]
(%i3) is(equal(x,z));
(%o3) true
(%i4) assume(a>=1,1>=a);
(%o4) [a >= 1, a <= 1]
(%i5) is(equal(a,1));
(%o5) true
(%i6) assume(b>1);
(%o6) [b > 1]
(%i7) is(equal(b,1));
(%o7) false
(%i8) is(notequal(b,1));
(%o8) true
I think %o3, %o5, %o7, and %o8 are all as expected, right?
}}}
So the real issue is that Sage's "==" is more at Maxima's equal(), while
Sage's "is" is more at Maxima's "=". Fixing this will probably require
some interesting futzing with the Maxima parser, though, since usually we
want == to become =, I think.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/1163#comment:10>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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