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7.7.2.0. centralizer
Procedure from library central.lib (see central_lib).

Usage:
centralizer(F, D[, N]); F poly/ideal, D int, N optional int

Return:
ideal, generated by computed elements

Purpose:
computes subalgebra generators of centralizer(F) up to degree D

Note:
In general, one cannot compute the whole centralizer(F).
Hence, one has to specify a termination condition via arguments D and/or N.
If D is positive, only centralizing elements up to degree D will be found.
If D is negative, the termination is determined by N only.
If N is given, the computation stops if at least N elements have been found.
Warning: if N is given and bigger than the actual number of generators,
the procedure may not terminate.
Current ordering must be a degree compatible well-ordering.

Example:
 
See also: center; inCentralizer.


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