From b615070ad95577d8faa8b4b96bac07d4e8ac4f1f Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Mon, 27 Jul 2020 16:17:18 -0500
Subject: [PATCH] Add Python bindings to one_group_xs

---
 openmc/lib/nuclide.py | 14 ++++++++++++++
 src/nuclide.cpp       | 12 ++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/openmc/lib/nuclide.py b/openmc/lib/nuclide.py
index 571dcc6551..4dd90f9cae 100644
--- a/openmc/lib/nuclide.py
+++ b/openmc/lib/nuclide.py
@@ -2,6 +2,9 @@ from collections.abc import Mapping
 from ctypes import c_int, c_double, c_char_p, POINTER, c_size_t
 from weakref import WeakValueDictionary
 
+from numpy.ctypeslib import ndpointer
+import numpy as np
+
 from ..exceptions import DataError, AllocationError
 from . import _dll
 from .core import _FortranObject
@@ -10,6 +13,8 @@ from .error import _error_handler
 
 __all__ = ['Nuclide', 'nuclides', 'load_nuclide']
 
+_array_1d_dble = ndpointer(dtype=np.double, ndim=1, flags='CONTIGUOUS')
+
 # Nuclide functions
 _dll.openmc_get_nuclide_index.argtypes = [c_char_p, POINTER(c_int)]
 _dll.openmc_get_nuclide_index.restype = c_int
@@ -20,6 +25,8 @@ _dll.openmc_load_nuclide.errcheck = _error_handler
 _dll.openmc_nuclide_name.argtypes = [c_int, POINTER(c_char_p)]
 _dll.openmc_nuclide_name.restype = c_int
 _dll.openmc_nuclide_name.errcheck = _error_handler
+_dll.openmc_nuclide_one_group_xs.argtypes = [c_int, c_int, _array_1d_dble,
+    _array_1d_dble, c_int, POINTER(c_double)]
 _dll.nuclides_size.restype = c_size_t
 
 
@@ -70,6 +77,13 @@ class Nuclide(_FortranObject):
         _dll.openmc_nuclide_name(self._index, name)
         return name.value.decode()
 
+    def one_group_xs(self, MT, energy, flux):
+        energy = np.asarray(energy, dtype=float)
+        flux = np.asarray(flux, dtype=float)
+        xs = c_double()
+        _dll.openmc_nuclide_one_group_xs(self._index, MT, energy, flux, len(flux), xs)
+        return xs.value
+
 
 class _NuclideMapping(Mapping):
     """Provide mapping from nuclide name to index in nuclides array."""
diff --git a/src/nuclide.cpp b/src/nuclide.cpp
index 66236441ff..d6da7d60f8 100644
--- a/src/nuclide.cpp
+++ b/src/nuclide.cpp
@@ -1043,6 +1043,18 @@ openmc_nuclide_name(int index, const char** name)
   }
 }
 
+extern "C" int
+openmc_nuclide_one_group_xs(int index, int MT, const double* energy, const double* flux, int n, double* xs)
+{
+  if (index < 0 || index >= data::nuclides.size()) {
+    set_errmsg("Index in nuclides vector is out of bounds.");
+    return OPENMC_E_OUT_OF_BOUNDS;
+  }
+
+  *xs = data::nuclides[index]->one_group_xs(MT, {energy, energy + n + 1}, {flux, flux + n});
+  return 0;
+}
+
 void nuclides_clear()
 {
   data::nuclides.clear();