SUBROUTINE H12(MODE,LPIVOT,L1,M,U,IUE,UP,C,ICE,ICV,NCV)
C***BEGIN PROLOGUE  H12
C***REFER TO  HFTI,LSEI,WNNLS
C
C     SUBROUTINE H12 (MODE,LPIVOT,L1,M,U,IUE,UP,C,ICE,ICV,NCV)
C
C     C.L.Lawson and R.J.Hanson, Jet Propulsion Laboratory, 1973 Jun 12
C     to appear in 'Solving Least Squares Problems', Prentice-Hall, 1974
C
C     Modified at SANDIA LABS, May 1977, to --
C
C     1)  Remove double precision accumulation, and
C     2)  Include usage of the Basic Linear Algebra Package for
C         vectors longer than a particular threshold.
C
C     Construction and/or application of a single
C     Householder transformation..     Q = I + U*(U**T)/B
C
C     MODE    = 1 or 2   to select algorithm  H1  or  H2 .
C     LPIVOT is the index of the pivot element.
C     L1,M   If L1 .LE. M   the transformation will be constructed to
C            zero elements indexed from L1 through M.   If L1 GT. M
C            THE SUBROUTINE DOES AN IDENTITY TRANSFORMATION.
C     U(),IUE,UP    On entry to H1 U() contains the pivot vector.
C                   IUE is the storage increment between elements.
C                                       On exit from H1 U() and UP
C                   contain quantities defining the vector U of the
C                   Householder transformation.   On entry to H2 U()
C                   and UP should contain quantities previously computed
C                   by H1.  These will not be modified by H2.
C     C()    On entry to H1 or H2 C() contains a matrix which will be
C            regarded as a set of vectors to which the Householder
C            transformation is to be applied.  On exit C() contains the
C            set of transformed vectors.
C     ICE    Storage increment between elements of vectors in C().
C     ICV    Storage increment between vectors in C().
C     NCV    Number of vectors in C() to be transformed. If NCV .LE. 0
C            no operations will be done on C().
C***ROUTINES CALLED  SAXPY,SDOT,SSWAP
C***END PROLOGUE  H12