MinimalSubalgebra(S) calculates the smallest Lie subalgebra containing the list of vectors S from a defined Lie algebra g. A list of basis vectors for the subalgebra from the Lie algebra g is returned.

MinimalSubalgebra(M) calculates the smallest matrix algebra containing the matrices in the list M.

The command MinimalSubalgebra is part of the DifferentialGeometry:-LieAlgebras package.  It can be used in the form MinimalSubalgebra(...) only after executing the commands with(DifferentialGeometry) and with(LieAlgebras), but can always be used by executing DifferentialGeometry:-LieAlgebras:-MinimalSubalgebra(...).