From 712352c8e1bc9cf427c223838f84b331aa0d140e Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Tue, 4 Jul 2017 15:06:33 -0500
Subject: [PATCH] Add optional instance argument for
 openmc_cell_set_temperature

---
 docs/source/capi/index.rst |  5 ++++-
 openmc/capi.py             | 11 +++++++++--
 src/api.F90                | 19 ++++++++++++++-----
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/docs/source/capi/index.rst b/docs/source/capi/index.rst
index c932bcde9..4cc195ef2 100644
--- a/docs/source/capi/index.rst
+++ b/docs/source/capi/index.rst
@@ -8,7 +8,7 @@ C API
 
    Run a stochastic volume calculation
 
-.. c:function:: int openmc_cell_set_temperature(int id, double T)
+.. c:function:: int openmc_cell_set_temperature(int id, double T, int* instance)
 
    Set the temperature of a cell.
 
@@ -16,6 +16,9 @@ C API
    :type id: int
    :param T: Temperature in Kelvin
    :type T: double
+   :param instance: Which instance of the cell. To set the temperature for all
+                    instances, pass a null pointer.
+   :type instance: int*
    :return: Return status (negative if an error occurred)
    :rtype: int
 
diff --git a/openmc/capi.py b/openmc/capi.py
index 2df55abce..ea6f1e7c9 100644
--- a/openmc/capi.py
+++ b/openmc/capi.py
@@ -66,7 +66,7 @@ class OpenMCLibrary(object):
         """Run stochastic volume calculation"""
         return self._dll.openmc_calculate_volumes()
 
-    def cell_set_temperature(self, cell_id, T):
+    def cell_set_temperature(self, cell_id, T, instance=None):
         """Set the temperature of a cell
 
         Parameters
@@ -75,9 +75,16 @@ class OpenMCLibrary(object):
             ID of the cell
         T : float
             Temperature in K
+        instance : int or None
+            Which instance of the cell
 
         """
-        return self._dll.openmc_cell_set_temperature(cell_id, T)
+        if instance is not None:
+            return self._dll.openmc_cell_set_temperature(
+                cell_id, T, byref(c_int(instance)))
+        else:
+            return self._dll.openmc_cell_set_temperature(cell_id, T, None)
+
 
     def finalize(self):
         """Finalize simulation and free memory"""
diff --git a/src/api.F90 b/src/api.F90
index 72879f41f..444dc71f9 100644
--- a/src/api.F90
+++ b/src/api.F90
@@ -41,12 +41,13 @@ contains
 ! OPENMC_CELL_SET_TEMPERATURE sets the temperature of a cell
 !===============================================================================
 
-  function openmc_cell_set_temperature(id, T) result(err) bind(C)
+  function openmc_cell_set_temperature(id, T, instance) result(err) bind(C)
     integer(C_INT), value, intent(in) :: id  ! id of cell
     real(C_DOUBLE), value, intent(in) :: T
+    integer(C_INT), optional, intent(in) :: instance
     integer(C_INT) :: err
 
-    integer :: i
+    integer :: i, n
 
     err = -1
     if (allocated(cells)) then
@@ -54,8 +55,16 @@ contains
         i = cell_dict % get_key(id)
         associate (c => cells(i))
           if (allocated(c % sqrtkT)) then
-            c % sqrtkT(:) = sqrt(K_BOLTZMANN * T)
-            err = 0
+            n = size(c % sqrtkT)
+            if (present(instance) .and. n > 1) then
+              if (instance >= 0 .and. instance < n) then
+                c % sqrtkT(instance + 1) = sqrt(K_BOLTZMANN * T)
+                err = 0
+              end if
+            else
+              c % sqrtkT(:) = sqrt(K_BOLTZMANN * T)
+              err = 0
+            end if
           end if
         end associate
       end if
@@ -92,7 +101,7 @@ contains
           id = materials(p % material) % id
         end if
       end if
-      instance = p % cell_instance
+      instance = p % cell_instance - 1
     end if
   end subroutine openmc_find