
7.10.6.26 ncrepIsDefined
Procedure from library ncrat.lib (see ncrat_lib).
 Usage:
 list l = ncrepIsDefined(q, vars, n, maxcoeff);
 Return:
 list(dim, list vars, list(A1, ..., Ak)), where:
If dim > 0 then there are matrices A1, ..., Ak of size dim
such that q is defined at A = (A1, ..., Ak), i.e.,
q.mat is invertible at A.
If dim = 0 then no such point was found.
 Note:
 Test whether q.mat is invertible via evaluation
at random matrix points with integer coefficients
in [maxcoeff, maxcoeff]. Stops after n tries.
Use iximatrix in ith try. The list vars contains the
nc variables which occur in q.
Example:
 LIB "ncrat.lib";
ncInit(list("x", "y"));
ncrat f = ncratFromString("inv(x*yy*x)");
ncrep q = ncrepGet(f);
ncrepIsDefined(q, list(x, y), 5, 10);
==> [1]:
==> 2
==> [2]:
==> [1]:
==> x
==> [2]:
==> y
==> [3]:
==> [1]:
==> _[1,1]=0
==> _[1,2]=9
==> _[2,1]=2
==> _[2,2]=7
==> [2]:
==> _[1,1]=8
==> _[1,2]=9
==> _[2,1]=4
==> _[2,2]=2
ncrat g = ncratFromString("inv(xx)");
ncrep r = ncrepGet(g);
ncrepIsDefined(r, list(x), 5, 10);
==> [1]:
==> 0
==> [2]:
==> [1]:
==> x
==> [3]:
==> empty list

