#5009: elementary_divisors for integer matrices: fix doc string
----------------------------+-----------------------------------------------
Reporter: jhpalmieri | Owner: was
Type: defect | Status: new
Priority: major | Milestone: sage-3.3
Component: linear algebra | Keywords: elementary divisor
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The doc string for the {{{elementary_divisors}}} method in
matrix_integer_dense.pyx says
{{{
The elementary divisors are the invariants of the finite
abelian group that is the cokernel of this matrix.
}}}
The word "cokernel" needs to be expanded upon. I think, from trial and
error, that this is computing the cokernel of left multiplication by the
matrix, and this needs to be '''clearly stated''', especially given other
left/right issues with matrices in Sage. (See #1587, for example.)
Furthermore, give at least one example where the matrix ''isn't square''
so we can see a bit more clearly on which side the matrix is acting, say a
simple matrix like [[3, 0, 0], [0, 0, 0]]. Maybe even include both this
and its transpose.
(As an editorial comment, I find it really annoying that methods like this
are for left multiplication, while methods like {{{restrict_codomain}}}
are for right multiplication, so if I want to use them both, I have to
take transposes way too many times.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5009>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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