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D.2.6.3 changevar

Procedure from library ring.lib (see ring_lib).

Usage:
changevar(newr,vars[,r]); newr,vars=strings, r=ring/qring

Create:
creates a new ring with name `newr` and makes it the basering if r is an existing ring/qring [default: r=basering].
The new ring differs from the old ring only in the variables. If, say, (newr,vars) = ("R","t()") and the ring r exists and has n variables, the new basering will have name R and variables t(1),...,t(n).
If vars = "a,b,c,d", the new ring will have the variables a,b,c,d.

Return:
No return value

Note:
This procedure is useful in connection with the procedure ringtensor, when a conflict between variable names must be avoided. This proc uses 'execute' or calls a procedure using 'execute'. If you use it in your own proc, let the local names of your proc start with @.

Example:
 
LIB "ring.lib";
ring r=0,(x,y,u,v),(dp(2),ds);
ideal i = x^2,y^2-u^3,v;
qring Q = std(i);
setring(r);
changevar("R","A()"); R; "";
==> // basering is now R
==> //   characteristic : 0
==> //   number of vars : 4
==> //        block   1 : ordering dp
==> //                  : names    A(1) A(2) 
==> //        block   2 : ordering ds
==> //                  : names    A(3) A(4) 
==> //        block   3 : ordering C
==> 
changevar("Q'","a,b,c,d",Q); Q';
==> // basering is now Q'
==> //   characteristic : 0
==> //   number of vars : 4
==> //        block   1 : ordering dp
==> //                  : names    a b 
==> //        block   2 : ordering ds
==> //                  : names    c d 
==> //        block   3 : ordering C
==> // quotient ring from ideal
==> _[1]=d
==> _[2]=a2
==> _[3]=b2-c3
kill R,Q,Q';
if(system("with","Namespaces")) {
if( nameof(Current) == "Ring" ) {
kill Top::R,Top::Q';
} else {
kill Ring::R,Ring::Q';
}
}


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