newRPL - build 1255 released! [updated to 1299]
12-19-2018, 07:44 PM
Post: #338
 Claudio L. Senior Member Posts: 1,885 Joined: Dec 2013
RE: newRPL - build 1089 released! [update:build 1127]
(12-19-2018 08:36 AM)The Shadow Wrote:  I'm not clear on why you need a symbol for the identity matrix for those particular rules? Matrices can be multiplied by a scalar just fine. EDIT: In fact, in standard linear algebra you *can't* add the identity matrix to a scalar.

You might well need the identity matrix in other contexts, though.

EDIT: Where problems do arise is in the rule eliminating an added zero. For matrices, that would have to be the zero matrix. But since you're getting rid of it anyway, maybe it's not too much of a problem?

I wonder if we need a separate MATRIXSIMPLIFY command?

I didn't think as far as the zero matrix, will be needed for sure. The identity in the example perhaps wasn't clear because I used the letter n in n*X+X, but I was thinking what if n is a matrix (replace it with A for visual impact)
Now A*X+X will become (A+ I) *X. The special symbol I should match whatever size allows the addition to matrix A to proceed. The only special thing is that is a matrix of all sizes. The zero matrix also needs a special all-sizes symbol in case you decided to EVAL or ->NUM the expression eventually. The zero only gets simplified if added to something, if it's by itself you can't remove it.
X-X = 0 (matrix symbol zero) and that result needs to be shown to the user. Problem is... What if the user does ->NUM? What size matrix would it be?
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