#10876: Create elementary matrices
-----------------------------------+----------------------------------------
Reporter: rbeezer | Owner: jason, was
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-4.7
Component: linear algebra | Keywords:
Author: Rob Beezer | Upstream: N/A
Reviewer: Karl-Dieter Crisman | Merged:
Work_issues: |
-----------------------------------+----------------------------------------
Changes (by rbeezer):
* status: needs_work => needs_review
Old description:
> Patch adds a matrix constructor to build elementary matrices, which
> correspond to row operations. These matrices are very useful when
> teaching properties of determinants.
>
> ----
> Apply attachment:trac_10876-elementary-matrices-v3.patch
New description:
Patch adds a matrix constructor to build elementary matrices, which
correspond to row operations. These matrices are very useful when
teaching properties of determinants.
----
Apply [attachment:trac_10876-elementary-matrices-v4.patch]
--
Comment:
Replying to [comment:10 kcrisman]:
> * Couldn't the following just be `n<=0`, since you catch that later?
Then you don't have to worry about the thing later.
> {{{
> if n < 0:
> raise ValueError('size of elementary matrix must be positive, not
{0}'.format(n))
> }}}
Yes. Changed this, edited error message, edited two doctests to conform.
> * I'd move the checks like
> {{{
> if row2 is None and scale is None:
> }}}
> to right after where you turn `col1` and `col2` into `row1` and
`row2`, to improve readability later.
I like these where they are. Lots of error-checking above to get right
inputs. Then the analysis of what we have makes the decision on which of
the three elementary matrix types to create. This is how we avoid
creating three functions in the global namespace. So I'd like to have it
divorced from the other stuff, and split off as the next step.
> * I think it might be possible to use simultaneous assignment for what
comes after
> {{{
> elif not row2 is None and scale is None:
> }}}
> in the same way that
> {{{
> a,b = 2,3
> }}}
Again, I like the four statements laid out like they are, I think the
symmetry of it is a bit easier to read.
> One more weird result:
> {{{
> sage: elementary_matrix(4,2,row1=1,row2=3)
> [1 0 0 0]
> [0 0 0 1]
> [0 0 1 0]
> [0 1 0 0]
> }}}
> If the first argument isn't a ring, you just automatically make the ring
the integer ring, the size the first argument, and ignore the second
argument. Probably this should be caught. Needs work :(
Fixed with new check as very first two lines of routine. New doctest
(first of error checks) will exercise it. Your example is caught as well.
> Oh, and you didn't capitalize a letter:
> {{{
> to determine the representation used. the default is ``False`` which
> }}}
Fixed.
Three for five. Hope that does it. Highest ratio of error-checks to code
ever, and a v4 patch is a new personal best. Thanks for your help - this
is much better than the original conception.
Rob
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10876#comment:12>
Sage <http://www.sagemath.org>
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