The most prominent of these (and historically the first) is the representation theory of groups, in which elements of a group are represented by invertible matrices in such a way that the group operation is matrix multiplication.
Den mest omfattende teori (og den historisk første) er repræsentationsteorien for grupper, hvor gruppeelementerne er repræsenteret af invertible matricer, således at gruppeoperationen svarer til matrixmultiplikation.