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D.4.2.5 alg_kernel

Procedure from library algebra.lib (see algebra_lib).

Usage:
alg_kernel(phi,pr[,s,c]); phi map to basering, pr preimage ring, s string (name of kernel in pr), c integer.

Return:
a string, the kernel of phi as string.
If, moreover, a string s is given, the algorithm creates, in the preimage ring pr the kernel of phi with name s.
Three different algorithms are used depending on c = 1,2,3. If c is not given or c=0, a heuristically best method is chosen. (algorithm 1 uses the preimage command)

Note:
Since the kernel of phi lives in pr, it cannot be returned to the basering. If s is given, the user has access to it in pr via s. The basering may be a quotient ring.

Example:
 


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