anchor.diff:      logical, intent (in), optional :: isSingularExpected
   
       double precision, dimension (3, 3) :: working
  -    double precision, dimension (3) :: ipiv
  +    integer, dimension (3) :: ipiv
       logical :: isNotComplainAboutSingular
   
       integer :: info
  
positive.code: 
      call getri(working, ipiv)
      inv = working
    end subroutine invMat
  
    subroutine calcVHT(vHT, Bx, By, Bz, vx, vy, vz)
      implicit none
  
negative.code:   ! But the matrix must be symmetric.
    subroutine invSymMat(inv, mat, isSingularExpected)
      use mkl95_precision, only: wp=>dp
      use lapack95, only: getrf, getri
      implicit none
  
      double precision, dimension (3, 3), intent (out) :: inv
  