#12809: Solve does not give consistent results when a dummy variable is involved
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Reporter: afleckenstein | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone: sage-5.0
Component: symbolics | Keywords: solve
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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When working on another ticket (#11201) that involves documentation for
the solve function, doing doctests proved to be frustrating. I added to
the examples section of the docstring, and then multiple tests failed. I
did some manual testing in sage and noticed a problem:
{{{
sage: var('x y')
(x, y)
sage: solve(cos(x)*sin(y)==1/2, x+y==0,x,y)
[[x == 1/4*pi + pi*z6, y == -1/4*pi - pi*z6]]
}}}
This is a perfectly valid answer, except that when I tried to solve the
same equations again, the answer is different:
{{{
sage: solve(cos(x)*sin(y)==1/2, x+y==0,x,y)
[[x == 1/4*pi + pi*z14, y == -1/4*pi - pi*z14]]
}}}
This is still mathematically correct.
If I solve them many more times, z's coefficient keeps going up by 8:
{{{
sage: solve(cos(x)*sin(y)==1/2, x+y==0,x,y)
[[x == 1/4*pi + pi*z22, y == -1/4*pi - pi*z22]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z30, y == -1/4*pi - pi*z30]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z38, y == -1/4*pi - pi*z38]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z46, y == -1/4*pi - pi*z46]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z54, y == -1/4*pi - pi*z54]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z62, y == -1/4*pi - pi*z62]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z70, y == -1/4*pi - pi*z70]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z78, y == -1/4*pi - pi*z78]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z86, y == -1/4*pi - pi*z86]]
sage: solve([cos(x)*sin(x) == 1/2, x+y == 0],x,y)
[[x == 1/4*pi + pi*z94, y == -1/4*pi - pi*z94]]
}}}
All still mathematically correct.
This is a problem when you are trying to add examples to the documentation
for solve and many doctests fail because the coefficients for the dummy
variable are shifted up by some integer amount. I have included the file
expressions_pyx_doctests.txt to show more of what I am talking about. To
cause this, I added two examples, and the examples that I added were not
complained about in the doctest. Also, z's coefficient went up by 6 this
time, different than 8 in the first example.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12809>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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