CoCoA » CoCoA-5

If N*X is valid (for N integer, and X of some type) then it makes perfect sense that -X should be equivalent to (-1)*X. We should also check that X*N is allowed and is equivalent to N*X.

I wonder if the equivalence can be implemented "automatically"?
[I have my doubts]

In any case, we should make sure that the equivalence is fully tested.

John Abbott wrote:

If N*X is valid (for N integer, and X of some type) then it makes perfect sense that -X should be equivalent to (-1)*X. We should also check that X*N is allowed and is equivalent to N*X.

I wonder if the equivalence can be implemented "automatically"?
[I have my doubts]

better not. That should be implemented at cocoalib level.

In any case, we should make sure that the equivalence is fully tested.

True: ... again should be done in cocoalib

I've just added operator- (scalar multiple by -1) to MatrixArith.

Contrary to my suggestion that multiplication by an integer be commutative, I notice that M*n is not yet offered in CoCoALib. Should it be added?

John Abbott wrote:

I've just added operator- (scalar multiple by -1) to MatrixArith.

Contrary to my suggestion that multiplication by an integer be commutative, I notice that M*n is not yet offered in CoCoALib. Should it be added?

yes, in fact

/**/ IdentityMat(R,2)*3;
ERROR: I don't know how to evaluate operator * between MAT and INT
IdentityMat(R,2)*3;
                ^

Added scalar multiplication on the right (for matrices) to CoCoALib.

Added scalar mult on the right & unary minus for matrices in C5.

Scalar multiplication could be useful for:

[LIST, MAT, MATRIXROW, RECORD, VECTOR]

JAA thinks it is better to exclude RECORD, at least initially.
At the moment the only operation on MATRIXROW is indexing (and printing). JAA would prefer not to have scalar multiples for MATRIXROW because he thinks that a MATRIXROW is a (read-only?) reference to a row in a matrix, and it would be unclear whether a scalar multiple of a MATRIXROW should modify the original matrix.

Can we create values of type VECTOR? Are they the same as ModuleElem in CoCoALib?

I agree to exclude MATRIXROW and RECORD

Can we create values of type VECTOR? Are they the same as ModuleElem in CoCoALib?

not yet. I think they sould be called ModuleElem in CoCoA-5 as well

If L is a list C5 cannot compute -L but it can compute (-1)*L and also L1-L2 if L1 and L2 are lists. This seems incongruous.
I tried implementing but couldn't figure out how: there is a commented out attempt in Interpreter.C:2168--2181.

Additonally, Anna questions how sensible it is to have "list arithmetic".

Is Giovanni willing to help, if we should decide to implement?