Compute the splitting points with threshold SPLTOL.
 SLARRA sets any "small" off-diagonal elements to zero.

          N is INTEGER
          The order of the matrix. N > 0.

          D is REAL array, dimension (N)
          On entry, the N diagonal elements of the tridiagonal
          matrix T.

          E is REAL array, dimension (N)
          On entry, the first (N-1) entries contain the subdiagonal
          elements of the tridiagonal matrix T; E(N) need not be set.
          On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT,
          are set to zero, the other entries of E are untouched.

          E2 is REAL array, dimension (N)
          On entry, the first (N-1) entries contain the SQUARES of the
          subdiagonal elements of the tridiagonal matrix T;
          E2(N) need not be set.
          On exit, the entries E2( ISPLIT( I ) ),
          1 <= I <= NSPLIT, have been set to zero

          SPLTOL is REAL
          The threshold for splitting. Two criteria can be used:
          SPLTOL<0 : criterion based on absolute off-diagonal value
          SPLTOL>0 : criterion that preserves relative accuracy

          TNRM is REAL
          The norm of the matrix.

          NSPLIT is INTEGER
          The number of blocks T splits into. 1 <= NSPLIT <= N.

          ISPLIT is INTEGER array, dimension (N)
          The splitting points, at which T breaks up into blocks.
          The first block consists of rows/columns 1 to ISPLIT(1),
          the second of rows/columns ISPLIT(1)+1 through ISPLIT(2),
          etc., and the NSPLIT-th consists of rows/columns
          ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.

          INFO is INTEGER
          = 0:  successful exit