```      SUBROUTINE SORM2L( SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC,
\$                   WORK, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
CHARACTER          SIDE, TRANS
INTEGER            INFO, K, LDA, LDC, M, N
*     ..
*     .. Array Arguments ..
REAL               A( LDA, * ), C( LDC, * ), TAU( * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  SORM2L overwrites the general real m by n matrix C with
*
*        Q * C  if SIDE = 'L' and TRANS = 'N', or
*
*        Q'* C  if SIDE = 'L' and TRANS = 'T', or
*
*        C * Q  if SIDE = 'R' and TRANS = 'N', or
*
*        C * Q' if SIDE = 'R' and TRANS = 'T',
*
*  where Q is a real orthogonal matrix defined as the product of k
*  elementary reflectors
*
*        Q = H(k) . . . H(2) H(1)
*
*  as returned by SGEQLF. Q is of order m if SIDE = 'L' and of order n
*  if SIDE = 'R'.
*
*  Arguments
*  =========
*
*  SIDE    (input) CHARACTER*1
*          = 'L': apply Q or Q' from the Left
*          = 'R': apply Q or Q' from the Right
*
*  TRANS   (input) CHARACTER*1
*          = 'N': apply Q  (No transpose)
*          = 'T': apply Q' (Transpose)
*
*  M       (input) INTEGER
*          The number of rows of the matrix C. M >= 0.
*
*  N       (input) INTEGER
*          The number of columns of the matrix C. N >= 0.
*
*  K       (input) INTEGER
*          The number of elementary reflectors whose product defines
*          the matrix Q.
*          If SIDE = 'L', M >= K >= 0;
*          if SIDE = 'R', N >= K >= 0.
*
*  A       (input) REAL array, dimension (LDA,K)
*          The i-th column must contain the vector which defines the
*          elementary reflector H(i), for i = 1,2,...,k, as returned by
*          SGEQLF in the last k columns of its array argument A.
*          A is modified by the routine but restored on exit.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A.
*          If SIDE = 'L', LDA >= max(1,M);
*          if SIDE = 'R', LDA >= max(1,N).
*
*  TAU     (input) REAL array, dimension (K)
*          TAU(i) must contain the scalar factor of the elementary
*          reflector H(i), as returned by SGEQLF.
*
*  C       (input/output) REAL array, dimension (LDC,N)
*          On entry, the m by n matrix C.
*          On exit, C is overwritten by Q*C or Q'*C or C*Q' or C*Q.
*
*  LDC     (input) INTEGER
*          The leading dimension of the array C. LDC >= max(1,M).
*
*  WORK    (workspace) REAL array, dimension
*                                   (N) if SIDE = 'L',
*                                   (M) if SIDE = 'R'
*
*  INFO    (output) INTEGER
*          = 0: successful exit
*          < 0: if INFO = -i, the i-th argument had an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
REAL               ONE
PARAMETER          ( ONE = 1.0E+0 )
*     ..
*     .. Local Scalars ..
LOGICAL            LEFT, NOTRAN
INTEGER            I, I1, I2, I3, MI, NI, NQ
REAL               AII
*     ..
*     .. External Functions ..
LOGICAL            LSAME
EXTERNAL           LSAME
*     ..
*     .. External Subroutines ..
EXTERNAL           SLARF, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          MAX
*     ..
*     .. Executable Statements ..
*
*     Test the input arguments
*
INFO = 0
LEFT = LSAME( SIDE, 'L' )
NOTRAN = LSAME( TRANS, 'N' )
*
*     NQ is the order of Q
*
IF( LEFT ) THEN
NQ = M
ELSE
NQ = N
END IF
IF( .NOT.LEFT .AND. .NOT.LSAME( SIDE, 'R' ) ) THEN
INFO = -1
ELSE IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) ) THEN
INFO = -2
ELSE IF( M.LT.0 ) THEN
INFO = -3
ELSE IF( N.LT.0 ) THEN
INFO = -4
ELSE IF( K.LT.0 .OR. K.GT.NQ ) THEN
INFO = -5
ELSE IF( LDA.LT.MAX( 1, NQ ) ) THEN
INFO = -7
ELSE IF( LDC.LT.MAX( 1, M ) ) THEN
INFO = -10
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'SORM2L', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
IF( M.EQ.0 .OR. N.EQ.0 .OR. K.EQ.0 )
\$   RETURN
*
IF( ( LEFT .AND. NOTRAN ) .OR. ( .NOT.LEFT .AND. .NOT.NOTRAN ) )
\$     THEN
I1 = 1
I2 = K
I3 = 1
ELSE
I1 = K
I2 = 1
I3 = -1
END IF
*
IF( LEFT ) THEN
NI = N
ELSE
MI = M
END IF
*
DO 10 I = I1, I2, I3
IF( LEFT ) THEN
*
*           H(i) is applied to C(1:m-k+i,1:n)
*
MI = M - K + I
ELSE
*
*           H(i) is applied to C(1:m,1:n-k+i)
*
NI = N - K + I
END IF
*
*        Apply H(i)
*
AII = A( NQ-K+I, I )
A( NQ-K+I, I ) = ONE
CALL SLARF( SIDE, MI, NI, A( 1, I ), 1, TAU( I ), C, LDC,
\$               WORK )
A( NQ-K+I, I ) = AII
10 CONTINUE
RETURN
*
*     End of SORM2L
*
END

```