1:  #include <petscsys.h>

  3: /*@C
  4:     PetscIsCloseAtTol - Returns whether the two floating point numbers
  5:        are close at given relative and absolute tolerances.

  7:     Input Parameter:
  8: +     a - first floating point number
  9: .     b - second floating point number
 10: .     rtol - relative tolerance
 11: +     atol - absolute tolerances

 13:     Notes: https://www.python.org/dev/peps/pep-0485

 15:     Level: beginner
 16: @*/
 17: PetscBool PetscIsCloseAtTol(PetscReal a,PetscReal b,PetscReal rtol,PetscReal atol)
 18: {
 19:   PetscReal diff;
 20:   /* NaN is not considered close to any other value, including NaN */
 21:   if (PetscIsNanReal(a) || PetscIsNanReal(b)) return PETSC_FALSE;
 22:   /* Fast path for exact equality or two infinities of same sign */
 23:   if (a == b) return PETSC_TRUE;
 24:   /* Handle two infinities of opposite sign */
 25:   if (PetscIsInfReal(a) || PetscIsInfReal(b)) return PETSC_FALSE;
 26:   /* Cannot error if tolerances are negative */
 27:   rtol = PetscAbsReal(rtol); atol = PetscAbsReal(atol);
 28:   /* The regular check for difference within tolerances */
 29:   diff = PetscAbsReal(b - a);
 30:   return ((diff <= PetscAbsReal(rtol * b)) || (diff <= PetscAbsReal(rtol * a)) || (diff <= atol)) ? PETSC_TRUE : PETSC_FALSE;
 31: }