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Feature #876

subst: allowed also for indets in the coeff ring

Added by John Abbott almost 8 years ago. Updated almost 8 years ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
enhancing/improving
Target version:
Start date:
07 May 2016
Due date:
% Done:

0%

Estimated time:
Spent time:

Description

Suppose we have a poly ring of the form QQ(a,b)[x,y] and I want to substitute b=a+1.
Currently subst refuses because b is not an indet of the ring.

Working around this is very cumbersome.

History

#1 Updated by John Abbott almost 8 years ago

Here is an example I was trying with Sandro Logar

QQa1 ::= QQ[a[1..6], alpha, beta];
QQa := NewFractionField(QQa1);
P ::= QQa[x,y,z], lex;
use P;

conica := ScalarProduct(support((x+y+z)^2), [a[i] | i in 1..6]);

cond1 := subst(conica, [[x,0], [y, 0], [z, 1]]);

--a6 := num(LC(a[6]));

-- GIVES ERROR !conica1 := subst(conica, a[6], 0);
conica1 := sum(first(monomials(conica), 5));

retta := alpha*x + beta*y;
retta;

I := ideal(conica1, retta);
RGB := ReducedGBasis(I);
indent(RGB);

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