#14965: FloatingPoint exception when multiplying matrix over QQ by vector over
SR
-------------------------------------+-------------------------------------
Reporter: dkrenn | Owner:
Type: defect | Status: needs_info
Priority: major | Milestone: sage-
Component: linear algebra | duplicate/invalid/wontfix
Keywords: matrix, vector, | Resolution:
mutliplication, floatingpoint | Merged in:
exception | Reviewers: Jeroen Demeyer
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: #16908 |
-------------------------------------+-------------------------------------
Description changed by nbruin:
Old description:
> The input
> {{{
> Z=1/3
> def matrix_entry(s,r):
> result = 0
> result += Z^(s-r)
> return result
> A = matrix([[matrix_entry(s,r) for r in range(1,22)] for s in
> range(1,22)])
> v = vector([(2/3)^s+x*(2/3+4/9*(2/3)^30)^s for s in range(1,22)])
> A*v
> }}}
> gives
> {{{
> Traceback (click to the left of this block for traceback)
> ...
> RuntimeError: Floating point exception
> }}}
> Since the matrix has entries in {{{QQ}}} and the vector entries in the
> symbolic ring, there should not be any floating point operations
> involved.
>
> The example starts to work if you take smaller matrices or other entries.
New description:
The input
{{{
Z=1/3
def matrix_entry(s,r):
result = 0
result += Z^(s-r)
return result
A = matrix([[matrix_entry(s,r) for r in range(1,22)] for s in
range(1,22)])
v = vector([(2/3)^s+x*(2/3+4/9*(2/3)^30)^s for s in range(1,22)])
A*v
}}}
gives
{{{
Traceback (click to the left of this block for traceback)
...
RuntimeError: Floating point exception
}}}
Since the matrix has entries in {{{QQ}}} and the vector entries in the
symbolic ring, there should not be any floating point operations involved.
The example starts to work if you take smaller matrices or other entries.
'''NOTE:'''
The way to trigger the bug from sage is now:
{{{
sage:
f=84644440725961403098463183554485799389772425728699536724546678651368471662755793858191462623325951275455550962101277270763335324980423888503086416881487600951168887632284102290001262851926718316596582705934285641705714110547524777517804311041930987129930496818273454551255885915706318740821679919000000000000000000000*x/422165920314471048721358275854632323285179941428330150821135511815100042994592631347355397175387243022779234708963662480477375868719044084318634583443223137428890926160543699705457864438134730545535596936604372279922247951010042249163649352110753480952771747316504857000652757440826179465253453626540111934123296968384641+2097152/10460353203;
sage: maxima_calculus(f)==0
FloatingPointError
}}}
--
--
Ticket URL: <http://trac.sagemath.org/ticket/14965#comment:9>
Sage <http://www.sagemath.org>
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