LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ sla_lin_berr()

subroutine sla_lin_berr ( integer  n,
integer  nz,
integer  nrhs,
real, dimension( n, nrhs )  res,
real, dimension( n, nrhs )  ayb,
real, dimension( nrhs )  berr 
)

SLA_LIN_BERR computes a component-wise relative backward error.

Download SLA_LIN_BERR + dependencies [TGZ] [ZIP] [TXT]

Purpose:
    SLA_LIN_BERR computes componentwise relative backward error from
    the formula
        max(i) ( abs(R(i)) / ( abs(op(A_s))*abs(Y) + abs(B_s) )(i) )
    where abs(Z) is the componentwise absolute value of the matrix
    or vector Z.
Parameters
[in]N
          N is INTEGER
     The number of linear equations, i.e., the order of the
     matrix A.  N >= 0.
[in]NZ
          NZ is INTEGER
     We add (NZ+1)*SLAMCH( 'Safe minimum' ) to R(i) in the numerator to
     guard against spuriously zero residuals. Default value is N.
[in]NRHS
          NRHS is INTEGER
     The number of right hand sides, i.e., the number of columns
     of the matrices AYB, RES, and BERR.  NRHS >= 0.
[in]RES
          RES is REAL array, dimension (N,NRHS)
     The residual matrix, i.e., the matrix R in the relative backward
     error formula above.
[in]AYB
          AYB is REAL array, dimension (N, NRHS)
     The denominator in the relative backward error formula above, i.e.,
     the matrix abs(op(A_s))*abs(Y) + abs(B_s). The matrices A, Y, and B
     are from iterative refinement (see sla_gerfsx_extended.f).
[out]BERR
          BERR is REAL array, dimension (NRHS)
     The componentwise relative backward error from the formula above.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.