anchor.diff:      end do
       end do
       sumKm_dotVm = sumKm_dotVm / nGrid
  -    KZero = sumKm_dotVm / nGrid
  +    KZero = sumKm / nGrid
       call invSymMat(invKZero, KZero, .true.)
       res = matmul(invKZero, sumKm_dotVm)
   
  
positive.code:     logical, intent (in), optional :: isSingularExpected
  
      double precision, dimension (3, 3) :: working
      double precision, dimension (3) :: ipiv
      logical :: isNotComplainAboutSingular
  
      integer :: info
  
negative.code: 
      call getri(working, ipiv)
      inv = working
    end subroutine invSymMat
  
    subroutine calcVHT(vHT, Bx, By, Bz, vx, vy, vz)
      implicit none
  