module pef {              # Find prediction-error filter (helix magic)
  use hconest
  use cgstep_mod
  use solver_smp_mod
contains
  subroutine find_pef( dd, aa, niter) {
    integer,          intent( in)  :: niter        # number of iterations
    type( filter)                  :: aa           # filter
    real,    dimension(:), pointer :: dd           # input data
    call hconest_init( dd, aa)
    call solver_smp(m=aa%flt, d=-dd, Fop=hconest_lop, stepper=cgstep, niter=niter, m0=aa%flt)
    call cgstep_close()
    }
}