Expose rand number to openmc.lib

docs/source/pythonapi/capi.rst

@@ -35,6 +35,7 @@ Functions
    next_batch
    num_realizations
    plot_geometry
+   prn
    property_map
    reset
    reset_timers

include/openmc/random_lcg.h

@@ -112,5 +112,13 @@ extern "C" uint64_t openmc_get_stride();
 
 extern "C" void openmc_set_stride(uint64_t new_stride);
 
+//==============================================================================
+//! Generate a pseudo-random number using OpenMC's RNG.
+//! @param seed Pseudorandom number seed pointer
+//! @return A random number between 0 and 1
+//==============================================================================
+
+extern "C" double openmc_prn(uint64_t* seed);
+
 } // namespace openmc
 #endif // OPENMC_RANDOM_LCG_H

openmc/lib/__init__.py

@@ -58,7 +58,7 @@ def _uwuw_enabled():
 from .mesh import *
 from .filter import *
 from .tally import *
-from .settings import settings
+from .settings import settings, prn
 from .math import *
 from .plot import *
 from .weight_windows import *

openmc/lib/settings.py

@@ -1,4 +1,4 @@
-from ctypes import c_int, c_int32, c_int64, c_double, c_char_p, c_bool, POINTER
+from ctypes import c_int, c_int32, c_int64, c_uint64, c_double, c_char_p, c_bool, POINTER, byref
 
 from . import _dll
 from .core import _DLLGlobal
@@ -14,6 +14,8 @@
 _dll.openmc_get_seed.restype = c_int64
 _dll.openmc_set_stride.argtypes = [c_int64]
 _dll.openmc_get_stride.restype = c_int64
+_dll.openmc_prn.argtypes = [POINTER(c_uint64)]
+_dll.openmc_prn.restype = c_double
 _dll.openmc_get_n_batches.argtypes = [POINTER(c_int), c_bool]
 _dll.openmc_get_n_batches.restype = c_int
 _dll.openmc_get_n_batches.errcheck = _error_handler
@@ -116,4 +118,23 @@ def get_batches(self, get_max_batches=True):
         return n_batches.value
 
 
+def prn(seed):
+    """Generate a pseudo-random number using OpenMC's RNG
+
+    Parameters
+    ----------
+    seed : int
+        Pseudorandom number seed (will be modified in place)
+
+    Returns
+    -------
+    tuple of (float, int)
+        Random number between 0 and 1, and the updated seed
+
+    """
+    c_seed = c_uint64(seed)
+    random_value = _dll.openmc_prn(byref(c_seed))
+    return random_value, c_seed.value
+
+
 settings = _Settings()

src/random_lcg.cpp

@@ -143,4 +143,9 @@ extern "C" void openmc_set_stride(uint64_t new_stride)
   prn_stride = new_stride;
 }
 
+extern "C" double openmc_prn(uint64_t* seed)
+{
+  return prn(seed);
+}
+
 } // namespace openmc

tests/unit_tests/test_lib.py

@@ -1045,3 +1045,26 @@ def test_sample_external_source(run_in_tmpdir, mpi_intracomm):
     openmc.lib.init(["-c"])
     openmc.lib.sample_external_source(100)
     openmc.lib.finalize()
+
+
+def test_prn(pincell_model, mpi_intracomm):
+    openmc.lib.init()
+
+    seed = 12345
+    random_numbers = []
+    for _ in range(10):
+        random_value, seed = openmc.lib.prn(seed)
+        random_numbers.append(random_value)
+        # Check that random values are in [0, 1)
+        assert 0.0 <= random_value < 1.0
+
+    # Check that we got different values (not all the same)
+    assert len(set(random_numbers)) > 1
+
+    # Check that using the same initial seed produces the same sequence
+    seed2 = 12345
+    for expected_value in random_numbers:
+        random_value, seed2 = openmc.lib.prn(seed2)
+        assert random_value == pytest.approx(expected_value)
+
+    openmc.lib.finalize()