SlepcCompareSmallestPosReal#

An eigenvalue comparison function used to sort according to the smallest positive real part.

Synopsis#

#include "slepcsys.h" 
PetscErrorCode SlepcCompareSmallestPosReal(PetscScalar ar,PetscScalar ai,PetscScalar br,PetscScalar bi,PetscInt *result,PetscCtx ctx)

Logically Collective

Input Parameters#

  • ar - real part of the 1st eigenvalue

  • ai - imaginary part of the 1st eigenvalue

  • br - real part of the 2nd eigenvalue

  • bi - imaginary part of the 2nd eigenvalue

  • ctx - user-defined context, not used here

Output Parameter#

  • result - result of comparison

Note#

This sorting criterion is used in the SVD for computing smallest singular values from the cyclic matrix. In that case, the computed values come in pairs \(\pm\lambda\). If the two values to compare have the same sign, the preferred one is the one with smallest magnitude. Otherwise, the prefered one is the rightmost (positive sign).

See Also#

SlepcEigenvalueComparisonFn, SlepcSCCompare(), SlepcSC

Level#

developer

Location#

src/sys/slepcsc.c

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