#10741: BinaryQF matrix actions are wrong
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Reporter: justin | Owner: justin
Type: defect | Status: new
Priority: major | Milestone:
Component: quadratic forms | Keywords: matrix, action, quadratic form
Author: justin | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Description changed by justin:
Old description:
> The code implementing the matrix_action_right() and matrix_action_left()
> is wrong.
>
> As an example, for right actions, associativity does not hold:
>
> sage: M=Matrix(ZZ,2,2,[1,-1,0,1])
> sage: N=Matrix(ZZ,2,2,[0,1,-1,0])
> sage: Q=BinaryQF(5,7,1)
> sage: Q.matrix_action_right(M).matrix_action_right(N)
> x^2 - 5*x*y - y^2
> sage: Q.matrix_action_right(M*N)
> 13*x^2 - 17*x*y + 5*y^2
>
> While the doc strings describe, in each case, the correct formulae, the
> code is "backwards": the left action should use the rows; the right
> action should use the columns.
New description:
The code implementing the matrix_action_right() and matrix_action_left()
is wrong.
As an example, for right actions, associativity does not hold:
{{{
sage: M=Matrix(ZZ,2,2,[1,-1,0,1])
sage: N=Matrix(ZZ,2,2,[0,1,-1,0])
sage: Q=BinaryQF(5,7,1)
sage: Q.matrix_action_right(M).matrix_action_right(N)
x^2 - 5*x*y - y^2
sage: Q.matrix_action_right(M*N)
13*x^2 - 17*x*y + 5*y^2
}}}
While the doc strings describe, in each case, the correct formulae, the
code is "backwards": the left action should use the rows; the right action
should use the columns.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10741#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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