SUBROUTINE VEC(M,N,A,LDA,B)
C  This routine vectorizes a matrix, B = vec(A):  B is a vector 
C  containing the columns of A stored successively with no gaps 
C  between columns.
C  Inputs:
C  M      Row dimension of matrix
C  N      Column dimension of matrix
C  A      Matrix to be vectorized
C  LDA    Leading dimension of A in calling program
C  Outputs:
C  B      Vectorized matrix; vector is of length MN.
      IMPLICIT REAL*8 (A-H,O-Z)
      DIMENSION A(LDA,100),B(500)
      IF((M.EQ.0).OR.(N.EQ.0))RETURN
      L=0
      DO 10 JN=1,N
      DO 10 IM=1,M
      L=L+1
   10 B(L)=A(IM,JN)
      RETURN
      END