More matrix features to MathObject matrices

[pstaabp]

This builds on #1012 and includes

• new methods for setting elements, removing columns and rows and a submatrix.
• A test suite for nearly all of the methods in the module.
• updated POD.

[Alex-Jordan]

I was looking at the POD since a lot of that is in the diff here, and I left some comments. But I'm going to pause because I think if you proofread the actual POD output you will see a lot of the same things that I'm seeing. I'll move on to testing the new tools now.

[Alex-Jordan]

I can't recall where, but there is somewhere else like this where we support having an explicit plus sign in front of the integer.

[Alex-Jordan]

But maybe this would be better if if actually accessed the dimensions of the matrix, and required an integer that is a valid row index.

[dpvc]

Since $i is usually a Perl real (not a string, for example), an initial plus sign will not be in its stringified version, so won't be part of the comparison in $i =~ m/.../ even if you used $M->row(+3). It would only be there if you passed the row number as a string, as in $M->row("+3"), which I might consider to be an improper value to pass (it is not a positive integer, it is a string).

[Alex-Jordan]

This has some issues as well. If I try it on a 1D matrix, I get an error:

$A = Matrix([ 1, 2, 3, 4 ]);
$B = $A->subMatrix([3]);

And if I try it on a 3D matrix, it is not returning what I would expect it to:

$A = Matrix([ [[1,2],[3,4]], [[5,6], [7,8]]]);
$B = $A->subMatrix([1], [1,2], [2]);
# $B seems to be what I would expect from subMatrix([1], [1,2], [1,2]);

[Alex-Jordan]

(It did seem to work when I tested with 2D matrices though.)

[pstaabp]

I thought of subMatrix only on 2D matrices, so will rework for other dimensions.

[pstaabp]

Rewrote this now. Should be working on non-2D matrices.

[drgrice1]

This needs to be

Suggested change

	my $el = $self->{data}[ $ind->[0] - 1 ];
	for my $i (1 .. scalar(@$ind) - 1) { $el = $el->{data}[ $ind->[$i] - 1 ]; }
	# update the value of $el
	$el = Value::makeValue($value);
	my $el = \($self->{data}[ $ind->[0] - 1 ]);
	for my $i (1 .. scalar(@$ind) - 1) { $el = \($$el->{data}[ $ind->[$i] - 1 ]); }
	# update the value of $el
	$$el = Value::makeValue($value);

	my $el = \($self->{data}[ $ind->[0] - 1 ]);
	for my $i (1 .. scalar(@$ind) - 1) { $el = \($$el->{data}[ $ind->[$i] - 1 ]); }

	# update the value of $el
	$$el = Value::makeValue($value);

in order to actually mutate the matrix.

[pstaabp]

Changed this, but odd that the test works for the previous version of the code as well as this one, however, I think the test needs some help.