CoCoA » CoCoALib

JAA: C4 has a function for creating an identity matrix. It also has a means of creating a zero matrix (of specified dimensions, NewMat). Presumably similar functions should exist in C5.

AMB: IdentityMat(QQ,2); and ZeroMat(QQ,2,4); [both in CoCoA-5 and in CoCoALib]
Should we have ZeroMat(ZZ,3); as a shortcut for ZeroMat(ZZ,3,3);?

JAA: If (when?) C5 has automatic promotion of ring elements then these functions can safely return a matrix over ZZ; otherwise the ring in which the entries reside will have to be specified explicitly as an argument.

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JAA: What would a function such as ConcatHor or ConcatVer or BlockMatrix do when given matrices whose elements belong to different rings? Will automatic promotion occur here too?

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JAA: Just a quick comment about the alternative matrix constructors MatrixByRows and MatrixByCols. JAA believes that both matrix dimensions should be given explicitly when using these ctors: at least one of the dimensions must be given explicitly, and to avoid doubt and confusion about which one, it seems simplest to require both (their product can also be used to check that the supplied list of entry values has the correct length). The presence or absence of an argument specifying the ring should be as for the standard matrix ctor (currently JAA+AMB are tending toward not specifying explicitly the ring).

AMB: MakeMatByRows(2,3,[1,2,3,4,5,6]); [in CoCoA-5]

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JAA: Consider the example below:

R ::= QQ[x,y,z];
M := matrix(R,[[1,x],[1,y]]);
Use S ::= ZZ/(7)[x,y];
M := matrix(R,[[1,x],[1,y]]); // cut-and-pasted

Here's another example which is close to a "nasty surprise":

R ::= QQ[x,y];
Use S ::= QQ[a,b];
x := 2; y := 3;
M := matrix(R,[[1,x],[1,y]]); // cut-and-pasted

This issue was under "CoCoA" instead of "CoCoALib".
I'm recovering these old and forgotten issues, so we reconsider them.

This issue is a bit strange -- it is now quite old, and of questionable relevance now.

Perhaps we should just close it?

MatByRows/Cols is now available in CoCoALib.

All other questions have been dealt with, more or less directly.