PROGRAM MATVEC
*
* Multiplies an (mxn) matrix A by an (nx1) vector X 
*
      INTEGER LDA
      PARAMETER(LDA = 30)
      REAL A, X, Y
      INTEGER N, I, J
      DIMENSION A(LDA,LDA), B(LDA), C(LDA)
      OPEN(UNIT=1,FILE='input.dat',STATUS='UNKNOWN')
      READ(1,*) N
      DO 10 I = 1,N
        READ(1,*) (A(I,J), J = 1,N)
        C(I) = 0.
   10 CONTINUE
      READ(1,*) (B(I), I = 1,N)
      CLOSE(1)
      CALL MTRVEC(LDA,N,A,B,C)
      OPEN(UNIT=2,FILE='output.dat',STATUS='UNKNOWN')
      WRITE(2,*) 'To diavusma eivai:'
      DO 20 I = 1,N
        WRITE(2,*) C(I)
   20 CONTINUE
      CLOSE(2)
      STOP
      END


      SUBROUTINE MTRVEC(LDA,NDIM,A,X,Y)
      REAL A(LDA,*), X(*), Y(*), S
      INTEGER NDIM, I, J
      DO 10 I = 1,NDIM
        Y(I) = 0.
   10 CONTINUE
C
C Matrix-vector multiplication using SAXPY over the 
C columns of A with length n.
C
      DO 20 J = 1,NDIM
        CALL SAXPY(NDIM,X(J),A(1,J),Y)
   20 CONTINUE
C
      RETURN
      END


      SUBROUTINE SAXPY(N,A,X,Y)
      INTEGER N, I
      REAL A, X(*), Y(*)
      DO 10 I = 1,N
        Y(I) = A * X(I) + Y(I)
 10   CONTINUE
      RETURN
      END