re-introduce higher-order interpolation

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

00:03:09

passed #211049
test_mpi

00:04:38

passed #211050
test_mpi_fftw

00:04:49

passed #211051
test_mpi_fftw_hdf5

00:06:19

66.0%