Project

General

Profile

Feature #37

matrix constructors

Added by Anna Maria Bigatti over 6 years ago. Updated 4 months ago.

Status:
Closed
Priority:
High
Assignee:
Category:
Data Structures
Target version:
Start date:
02 Nov 2011
Due date:
% Done:

100%

Estimated time:
5.00 h
Spent time:

Description

Comments about matrix constructors: mainly "ring or not ring?"

IdentityMat(QQ,2), ZeroMat(QQ,2,4), ConcatHor, ConcatVer,
MatrixByRows, MatrixByCols, ....


Related issues

Related to CoCoA-5 - Feature #309: (Multi)BlockMatrixClosed2013-02-13

Related to CoCoA-5 - Design #1116: Port RowMat, ColMat, MatByRows,... to CoCoA-5New2017-11-06

History

#1 Updated by Anna Maria Bigatti over 6 years ago

  • Subject changed from matrix constructor to matrix constructors

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.

----------------------------------------------------------------------
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?

----------------------------------------------------------------------
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]

----------------------------------------------------------------------
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

The creation of the matrix M will not work as one might reasonably expect (i.e. creating a matrix whose entries are in R): it will produce an error.
If the ring were not supplied as an argument then M would contain a matrix whose entries lie in S; this might be what was wanted, but it is different from the original matrix!

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

Here the matrix construction will presumably succeed, but will not produce the original matrix. It is also easy to create examples producing the wrong result, if we change the definition of the ring R...

#2 Updated by Anna Maria Bigatti over 6 years ago

  • Category set to Philosophy

#3 Updated by Anna Maria Bigatti 12 months ago

  • Project changed from CoCoA to CoCoALib
  • Category deleted (Philosophy)
  • Target version set to CoCoALib-0.99560

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

#4 Updated by John Abbott 6 months ago

  • Category set to Data Structures

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

Perhaps we should just close it?

#5 Updated by Anna Maria Bigatti 6 months ago

  • % Done changed from 50 to 90

MatByRows/Cols is now available in CoCoALib.

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

#6 Updated by Anna Maria Bigatti 6 months ago

  • Related to Design #1116: Port RowMat, ColMat, MatByRows,... to CoCoA-5 added

#7 Updated by John Abbott 4 months ago

  • Status changed from In Progress to Closed
  • % Done changed from 90 to 100

Also available in: Atom PDF