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Feature #1469

Get indexed indets from a polyring

Added by John Abbott almost 4 years ago. Updated over 3 years ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
CoCoA-5 function: new
Target version:
CoCoA-5.4.2
Start date:
25 Jun 2020
Due date:
% Done:

0%

Estimated time:
Spent time:
0.60 h

Description

The using feature of CoCoA-4 has been removed in CoCoA-5. This can cause awkwardness when the ring to be used contains indets with indices.

The function indets(P,str) does not solve the matter nicely.

Make a function which make accessing indets with indexes easy. I am thinking of something like this:

P ::= QQ[x,y[1..3,1..3]];
y := IndetMap(P,"y");
y[2,2];  --> gives what you would expect

Another (contrived) example:

P ::= QQ[a[2],a[1],a[3]];
a := IndetMap(P,"a");
a[2]; --> gives 1st indet in P

Related issues

Related to CoCoA-5 - Design #292: Rename IndetsCalled to indetsClosed2013-01-17

Related to CoCoALib - Feature #1470: Get indexed indets from a polyringNew2020-06-25

Related to CoCoA-5 - Feature #723: Referring to indets with multiple indices from a polyringNew2015-06-02

History

#1 Updated by John Abbott almost 4 years ago

Note that CoCoA-5 already has the (undocumented?!?) type INTMAP which does exactly what we want.

Just need to make it accessible via a function (and possibly lift any weird restrictions that might have been imposed?).
I wonder where the source code is... somewhere inside the interpreter (see near line 519).

JAA has just checked that an INTMAP may be assigned and passed as a parameter.

#2 Updated by John Abbott almost 4 years ago

There should probably be a similar fn available in CoCoALib; this implies that we'll need a type for INTMAP.

#3 Updated by John Abbott almost 4 years ago

  • Related to Design #292: Rename IndetsCalled to indets added

#4 Updated by John Abbott almost 4 years ago

  • Related to Feature #1470: Get indexed indets from a polyring added

#5 Updated by John Abbott over 3 years ago

  • Related to Feature #723: Referring to indets with multiple indices from a polyring added

#6 Updated by Julian Danner over 3 years ago

Hi,
I would highly appreciate such a function, however I think it would be even better if one must not first initialize the variables, but could access them directly through the rings name P.
E.g. I would like to write 

P::= QQ[x,y[1..3,1..3]];
P.y[2,2];  --> gives what you would expect
similar to what one could do with :: in CoCoA-4. (This could simplify the code without impact on readability.)

I wrote a function that follows this idea called inject and it can be found as part of the apcocoa-packages here: https://git.fim.uni-passau.de/walsh/apcocoa-packages/-/blob/master/apcocoa/misc.cpkg5 with examples on usage in https://git.fim.uni-passau.de/walsh/apcocoa-packages/-/blob/master/tests/misc.cocoa5. My function returns a record that stores the indets inside nested lists. The only limitation here is that it only works for strictly positive indices.
Using my function one can write the above example as follows:

P::= QQ[x,y[1..3,1..3]];
P:=inject(P);
P.y[2,2];  --> gives what you would expect
In particular it is not required to write any other lines to be able to access possible other indets. (And the original ring can be found in P.ring_.)

But in any case, just having this IndetMap would also be fine for me, since I could adapt my implementation to be correct in general (by replacing each field-entry with the corresponding INTMAP).

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