Close #351 Expose global Seed

CHANGELOG.md

@@ -16,6 +16,8 @@ This is the 5th release candidate, a *pre-beta* version.
    [#320](https://github.com/ComputationalRadiationPhysics/picongpu/pull/320/files#diff-1)  
  - removed double `#define __COHERENTINCOHERENTWEIGHTING__ 1` in some example radiationConfig.param
    [#323](https://github.com/ComputationalRadiationPhysics/picongpu/pull/323/files)
+ - new file: `seed.param` allows to vary the starting conditions of "identical" runs
+   [#353](https://github.com/ComputationalRadiationPhysics/picongpu/pull/353)
 
 **New Features:**
  - Radiation plugin: add optional window functions to reduce ringing effects

src/libPMacc/include/mpi/SeedPerRank.hpp

@@ -0,0 +1,63 @@
+/**
+ * Copyright 2014 Axel Huebl
+ *
+ * This file is part of PIConGPU.
+ *
+ * PIConGPU is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PIConGPU is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with PIConGPU.
+ * If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "types.h"
+#include "Environment.hpp"
+
+namespace PMacc
+{
+namespace mpi
+{
+    /** Calculate a Seed per Rank
+     *
+     * This functor derives a unqiue seed for each MPI rank (or GPU) from
+     * a given global seed in a deterministic manner.
+     *
+     * \tparam T_DIM Dimensionality of the simulation (1-3 D)
+     */
+    template <unsigned T_DIM>
+    struct SeedPerRank
+    {
+        /** Functor implementation
+         *
+         * This method provides a guaranteed unique number per MPI rank
+         * (or GPU). When a (only locally unique) localShift parameter is used
+         * it is furthermore guaranteed that this number does not collide
+         * with an other seed.
+         *
+         * \param seed initial seed to vary two identical simulations
+         * \param localShift e.g. a unique species id
+         * \return uint32_t seed
+         */
+        uint32_t
+        operator()( uint32_t seed, uint32_t localShift = 0 )
+        {
+            PMACC_AUTO(&gc, PMacc::Environment<T_DIM>::get().GridController());
+
+            seed ^= gc.getGlobalSize( ) * localShift +
+                    gc.getGlobalRank( );
+            return seed;
+        }
+    };
+
+} /* namespace mpi */
+} /* namespace picongpu */

src/picongpu/include/particles/Particles.tpp

@@ -38,6 +38,7 @@
 #include "particles/memory/buffers/ParticlesBuffer.hpp"
 #include "ParticlesInit.kernel"
 #include "mappings/simulation/GridController.hpp"
+#include "mpi/SeedPerRank.hpp"
 
 #include "simulationControl/MovingWindow.hpp"
 
@@ -193,9 +194,9 @@ void Particles<T_ParticleDescription>::initFill( uint32_t currentStep )
     DataSpace<simDim> gpuCellOffset = simBox.getGlobalOffset( );
     gpuCellOffset.y( ) += window.slides * localCells.y( );
 
-
-    uint32_t seed = Environment<simDim>::get().GridController().getGlobalSize( ) * FrameType::CommunicationTag
-        + Environment<simDim>::get().GridController().getGlobalRank( );
+    GlobalSeed globalSeed;
+    mpi::SeedPerRank<simDim> seedPerRank;
+    uint32_t seed = seedPerRank( globalSeed(), FrameType::CommunicationTag );
     seed ^= POSITION_SEED;
     dim3 block( MappingDesc::SuperCellSize::getDataSpace( ) );
 
@@ -249,8 +250,9 @@ void Particles<T_ParticleDescription>::deviceAddTemperature( float_X energy )
     dim3 block( MappingDesc::SuperCellSize::getDataSpace( ) );
     DataSpace<simDim> superCells = this->particlesBuffer->getSuperCellsCount( );
 
-    uint32_t seed = Environment<simDim>::get().GridController().getGlobalSize( ) * FrameType::CommunicationTag
-        + Environment<simDim>::get().GridController().getGlobalRank( );
+    GlobalSeed globalSeed;
+    mpi::SeedPerRank<simDim> seedPerRank;
+    uint32_t seed = seedPerRank( globalSeed(), FrameType::CommunicationTag );
     seed ^= TEMPERATURE_SEED;
 
     __picKernelArea( kernelAddTemperature, this->cellDescription, CORE + BORDER + GUARD )

src/picongpu/include/simulation_defines/_defaultParam.loader

@@ -42,4 +42,4 @@
 #include "simulation_defines/param/radiationConfig.param"
 #include "simulation_defines/param/fieldBackground.param"
 #include "simulation_defines/param/radiationObserver.param"
-
+#include "simulation_defines/param/seed.param"

src/picongpu/include/simulation_defines/param/seed.param

@@ -0,0 +1,43 @@
+/**
+ * Copyright 2014 Axel Huebl
+ *
+ * This file is part of PIConGPU.
+ *
+ * PIConGPU is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PIConGPU is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with PIConGPU.
+ * If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+#pragma once
+
+namespace picongpu
+{
+    /** global seed
+     *
+     *  global seed to derive GPU local seeds from
+     *  - vary it to shuffle pseudo random generators for exactly same simulation
+     *  - note: even when kept constant, highly parallel simulations do not ensure
+     *          100% deterministic simulations on the floating point level
+     */
+    struct GlobalSeed
+    {
+        uint32_t
+        operator()()
+        {
+            /** to vary (binary) identical simulations, use a combination of
+             *  time(NULL) from \see <time.h> (precision: seconds) */
+            return 42;
+        }
+    };
+} /* namespace picongpu */