therwise, P is not used.

  A       (input) DOUBLE PRECISION array, dimension (LDA,N)
          The leading N-by-N part of this array must contain the
          state matrix A of the descriptor system.

  LDA     INTEGER
          The leading dimension of array A.  LDA &gt;= MAX(1,N).

  E       (input) DOUBLE PRECISION array, dimension (LDE,N)
          The leading N-by-N part of this array must contain the
          matrix E of the descriptor system.

  LDE     INTEGER
          The leading dimension of a