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slanv2

 NAME
      SLANV2 - compute the Schur factorization of a real 2-by-2
      nonsymmetric matrix in standard form

 SYNOPSIS
      SUBROUTINE SLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS,
                         SN )

          REAL           A, B, C, CS, D, RT1I, RT1R, RT2I, RT2R,
                         SN

 PURPOSE
      SLANV2 computes the Schur factorization of a real 2-by-2
      nonsymmetric matrix in standard form:

           [ A  B ] = [ CS -SN ] [ AA  BB ] [ CS  SN ]
           [ C  D ]   [ SN  CS ] [ CC  DD ] [-SN  CS ]

      where either
      1) CC = 0 so that AA and DD are real eigenvalues of the
      matrix, or 2) AA = DD and BB*CC < 0, so that AA + or -
      sqrt(BB*CC) are complex conjugate eigenvalues.

 ARGUMENTS
      A       (input/output) REAL
              B       (input/output) REAL C       (input/output)
              REAL D       (input/output) REAL On entry, the ele-
              ments of the input matrix.  On exit, they are
              overwritten by the elements of the standardized
              Schur form.

      RT1R    (output) REAL
              RT1I    (output) REAL RT2R    (output) REAL RT2I
              (output) REAL The real and imaginary parts of the
              eigenvalues. If the eigenvalues are both real,
              abs(RT1R) >= abs(RT2R); if the eigenvalues are a
              complex conjugate pair, RT1I > 0.

      CS      (output) REAL
              SN      (output) REAL Parameters of the rotation
              matrix.