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Combine matr_ass_* concepts linearly, with real or complex coefficients.

This operator also makes it possible to perform linear combinations by considering only the real or imaginary part of a matrix with complex coefficients (extraction of the real or complex part of a matrix).

All the matrix_*concepts to be combined must share**the same numbering**, that is, the two matrices will have been assembled by the ASSE_MATRICE operator with the same concept argument for the NUME_DDL keyword (cf. [U4.61.11]).

Produces a matr_asse_* data structure.