re-introduce higher-order interpolation

4 jobs for line_search in 6 minutes and 19 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed test_min #211048

00:03:09

passed test_mpi #211049

00:04:38

passed test_mpi_fftw #211050

00:04:49

passed test_mpi_fftw_hdf5 #211051

00:06:19

66.0%