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Feature #1644

Allow user to choose whether to print finite field elems as symm residues or non-neg residue

Added by John Abbott over 2 years ago. Updated about 2 years ago.

Status:
In Progress
Priority:
Normal
Assignee:
-
Category:
CoCoA-5 function: new
Target version:
CoCoA-5.4.2
Start date:
13 Jan 2022
Due date:
% Done:

10%

Estimated time:
Spent time:
0.85 h

Description

A student here asked how to make CoCoA-5 print elements of a finite field as the least non-neg residue class representative.

CoCoALib allows this, but CoCoA-5 does not.

History

#1 Updated by John Abbott over 2 years ago

JAA thinks that allowing the user to choose should not cause any problems: it is just a matter of printing.

Mmm, well, what should AsINT produce?

#2 Updated by John Abbott over 2 years ago

The current impl in SmallFpImpl.H expects there to be a boolean data mem which says how to print (LeastNonNeg or Symm).
The choice is fixed at creation time of the ring. The flag affects only the mem fn myExport.

Do we want to allow a global variable which is consulted each time a value is exported?

Maybe we need a 3-way flag: LeastNonNeg, Symm, UseGlobalSetting ?

SOURCE: Consult source code in SmallFpImpl.H

#3 Updated by John Abbott over 2 years ago

I have just given a demo to my students of using CRT to reconstruct a large integer value.
The demo happened to work well because AsINT returns "symmetric" representatives when
applied to elements of a finite field. Naturally, it did not work do well when I used the
prime 2. Technically this is my fault (since I should have checked what AsINT does).

Maybe there should be 2 fns instead of (or as well as?) AsINT for elements of a finite field.
For instance: SymmRepr and LeastNonNegRepr.

#4 Updated by John Abbott over 2 years ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 10

Anna suggests these names: AsINT_Symm and AsINT_NonNeg (because AsINT_LeastNonNeg is too long)
The idea is to have a name "similar" to AsINT.

UPDATE AsINT_symm and AsINT_NonNeg would give error if applied to an element of a ring of char 0... right?

#5 Updated by John Abbott about 2 years ago

The idea seems reasonable, but what names should we use?
  • AsINT_symm or AsINT_Symm
  • AsINT_NonNeg or AsINT_nonneg or AsINT_nneg

Other suggestions?

#6 Updated by John Abbott about 2 years ago

  • Target version changed from CoCoA-5.4.0 to CoCoA-5.4.2

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