Add Tutorials' Timesteps section

docs/user_guide/source/tutorials/basicTutorials.rst

@@ -7,3 +7,4 @@ Basic Tutorials
    variables
    attributes
    operators
+   timesteps

docs/user_guide/source/tutorials/overview.rst

@@ -12,3 +12,4 @@ More specifically, we will go through the following examples:
    2. :ref:`Array Variables <sec:tutorials_basics_variables>`
    3. :ref:`Attributes <sec:tutorials_basics_attributes>`
    4. :ref:`Operators <sec:tutorials_basics_operators>`
+   5. :ref:`Timesteps <sec:tutorials_basics_timesteps>`

docs/user_guide/source/tutorials/timesteps.rst

@@ -0,0 +1,203 @@
+Timesteps
+=========
+
+.. _sec:tutorials_basics_timesteps:
+
+In the previous tutorial, we introduced the concept of operators, and briefly touched upon the concept of timesteps.tutorial
+
+In this tutorial, we will explore how to write data for multiple timesteps, and how to read them back.
+
+So let's dig in!
+
+Start editing the skeleton file `ADIOS2/examples/hello/bpTimeWriteRead/bpTimeWriteRead_tutorialSkeleton.cpp <https://github.com/ornladios/ADIOS2/blob/master/examples/hello/bpTimeWriteRead/bpTimeWriteRead_tutorialSkeleton.cpp>`_.
+
+1. In an MPI application first we need to always initialize MPI. We do that with the following lines:
+
+.. code-block:: cpp
+
+   int rank, size;
+   int rank, size;
+   int provided;
+
+   // MPI_THREAD_MULTIPLE is only required if you enable the SST MPI_DP
+   MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided);
+   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+   MPI_Comm_size(MPI_COMM_WORLD, &size);
+
+2. This application has an optional command line argument for engine being used. If
+   no argument is provided, the default engine is BPFile.
+
+.. code-block:: cpp
+
+    const std::string engine = argv[1] ? argv[1] : "BPFile";
+
+3. We will define the number of timesteps and the size of the data that we will create.
+
+.. code-block:: cpp
+
+    const std::string filename = engine + "TimeWriteRead.bp";
+    const unsigned int nSteps = 10;
+    const unsigned int Nx = 60000;
+
+4. Now we need to create an ADIOS2 instance.
+
+.. code-block:: cpp
+
+   adios2::ADIOS adios(MPI_COMM_WORLD);
+
+5. Now we will populate the writer function with the following signature:
+
+.. code-block::
+
+   void writer(adios2::ADIOS &adios, const std::string &engine, const std::string &fname,
+             const size_t Nx, unsigned int nSteps, int rank, int size)
+   {
+     ...
+   }
+
+6. Let's create some simulation data. We will create a 1D array of size Nx, and fill it with 0.block
+
+.. code-block:: cpp
+
+   std::vector<double> simData(Nx, 0.0);
+
+7. Now we will create an IO object and set the engine type.block
+
+.. code-block:: cpp
+
+   adios2::IO bpIO = adios.DeclareIO("SimulationOutput");
+   io.SetEngine(engine);
+
+.. note::
+
+   The beauty of ADIOS2 is that you write the same code for all engines. The only thing that changes is the engine name.
+   The underlying engine handles all the intricacies of the engine's format, and the user enjoys the API's simplicity.
+
+8. Now we will create a variable for the simulation data and the time step.
+
+.. code-block:: cpp
+
+    const adios2::Dims shape{static_cast<size_t>(size * Nx)};
+    const adios2::Dims start{static_cast<size_t>(rank * Nx)};
+    const adios2::Dims count{Nx};
+    auto bpFloats = bpIO.DefineVariable<float>("bpFloats", shape, start, count);
+
+    auto bpTimeStep = bpIO.DefineVariable<unsigned int>("bpTimeStep");
+
+9. Now we will open the file for writing.
+
+.. code-block:: cpp
+
+    adios2::Engine bpWriter = bpIO.Open(fname, adios2::Mode::Write);
+
+10. Now we will write the data for each time step.
+
+.. code-block:: cpp
+
+   for (unsigned int step = 0; step < nSteps; ++step)
+   {
+       const adios2::Box<adios2::Dims> sel({0}, {Nx});
+       bpFloats.SetSelection(sel);
+
+       bpWriter.BeginStep();
+       bpWriter.Put(bpFloats, simData.data());
+       bpWriter.Put(bpTimeStep, step);
+       bpWriter.EndStep();
+
+       // Update values in the simulation data
+       update_array(simData, 10);
+   }
+
+11. Now we will close the file.
+
+.. code-block:: cpp
+
+   bpWriter.Close();
+
+12. Now we will populate the reader function with the following signature:
+
+.. code-block:: cpp
+
+   void reader(adios2::ADIOS &adios, const std::string &engine, const std::string &fname,
+               const size_t Nx, unsigned int /*nSteps*/, int rank, int /*size*/)
+   {
+     ...
+   }
+
+13. Now we will create an IO object and set the engine type.
+
+.. code-block:: cpp
+
+   adios2::IO bpIO = adios.DeclareIO("SimulationOutput");
+   io.SetEngine(engine);
+
+14. Now we will open the file for reading.
+
+.. code-block:: cpp
+
+   adios2::Engine bpReader = bpIO.Open(fname, adios2::Mode::Read);
+
+15. Now we will create a vector to store simData and a variable for the time step.
+
+.. code-block:: cpp
+
+   std::vector<float> simData(Nx, 0);
+   unsigned int timeStep = 0;
+
+16. Now we will read the data for each time step.
+
+.. code-block:: cpp
+
+   for (unsigned int step = 0; bpReader.BeginStep() == adios2::StepStatus::OK; ++step)
+   {
+       auto bpFloats = bpIO.InquireVariable<float>("bpFloats");
+       if (bpFloats)
+       {
+           const adios2::Box<adios2::Dims> sel({{Nx * rank}, {Nx}});
+           bpFloats.SetSelection(sel);
+           bpReader.Get(bpFloats, simData.data());
+       }
+       auto bpTimeStep = bpIO.InquireVariable<unsigned int>("bpTimeStep");
+       if (bpTimeStep)
+       {
+           bpReader.Get(bpTimeStep, &timeStep);
+       }
+
+       bpReader.EndStep();
+   }
+
+17. Now we will close the file.
+
+.. code-block:: cpp
+
+   bpReader.Close();
+
+18. Now we will call the writer and reader functions:
+
+.. code-block:: cpp
+
+   writer(adios, engine, filename, Nx, nSteps, rank, size);
+   reader(adios, engine, filename, Nx, nSteps, rank, size);
+
+19. Finally we need to finalize MPI.
+
+.. code-block:: cpp
+
+   MPI_Finalize();
+
+20. The final code should look as follows (excluding try/catch and optional usage of MPI), and it was derived from the
+    example `ADIOS2/examples/hello/bpTimeWriteRead/bpTimeWriteRead.cpp <https://github.com/ornladios/ADIOS2/blob/master/examples/hello/bpTimeWriteRead/bpTimeWriteRead.cpp>`_.
+
+.. literalinclude:: ../../../../examples/hello/bpTimeWriteRead/bpTimeWriteRead.cpp
+   :language: cpp
+
+21. You can compile and run it as follows:
+
+.. code-block:: bash
+
+   cd Path-To-ADIOS2/examples/hello/bpTimeWriteRead
+   mkdir build
+   cd build
+   cmake -DADIOS2_DIR=Path-To-ADIOS2/build/ ..
+   cmake --build .
+   ./adios2_hello_bpTimeWriteRead_mpi

examples/hello/bpTimeWriteRead/bpTimeWriteRead_tutorialSkeleton.cxx

@@ -0,0 +1,98 @@
+/*
+ * Distributed under the OSI-approved Apache License, Version 2.0.  See
+ * accompanying file Copyright.txt for details.
+ *
+ * bpTimeWriteRead.cpp  Simple example of writing and reading data through ADIOS2 BP engine with
+ * multiple simulations steps for every IO step.
+ *
+ *  Created on: Feb 16, 2017
+ *      Author: William F Godoy godoywf@ornl.gov
+ */
+
+#include <algorithm> //std::for_each
+#include <ios>       //std::ios_base::failure
+#include <iostream>  //std::cout
+#include <mpi.h>
+#include <stdexcept> //std::invalid_argument std::exception
+#include <vector>
+
+#include <adios2.h>
+
+void update_array(std::vector<float> &array, int val)
+{
+    std::transform(array.begin(), array.end(), array.begin(),
+                   [val](float v) -> float { return v + static_cast<float>(val); });
+}
+
+void writer(adios2::ADIOS &adios, const std::string &engine, const std::string &fname,
+            const size_t Nx, unsigned int nSteps, int rank, int size)
+{
+    // Add code to create the simulation data
+
+    // Add code to create ADIOS io and set engine type
+
+    // Add code to define sim data variable
+
+    // Add code to define time step variable
+
+    // Add code to open file
+
+    // Add code to write data across multiple steps, and update the simulation data
+
+    // Add code to close file
+}
+
+void reader(adios2::ADIOS &adios, const std::string &engine, const std::string &fname,
+            const size_t Nx, unsigned int /*nSteps*/, int rank, int /*size*/)
+{
+    // Add code to create ADIOS io and set engine type
+
+    // Add code to open file
+
+    // Add code to create variable for sim data and time step
+
+    // Add code to read data across multiple steps
+
+    // Add code to close file
+}
+
+int main(int argc, char *argv[])
+{
+    int rank, size;
+    int provided;
+
+    // Add code to initialize MPI
+
+    const std::string engine = argv[1] ? argv[1] : "BPFile";
+    std::cout << "Using engine " << engine << std::endl;
+
+    // Add Code to set filename, nSteps, Nx
+    try
+    {
+        // Add code to create ADIOS object
+
+        // Add code to call writer
+        // Add code to call reader
+    }
+    catch (std::invalid_argument &e)
+    {
+        std::cout << "Invalid argument exception, STOPPING PROGRAM from rank " << rank << "\n";
+        std::cout << e.what() << "\n";
+    }
+    catch (std::ios_base::failure &e)
+    {
+        std::cout << "IO System base failure exception, STOPPING PROGRAM "
+                     "from rank "
+                  << rank << "\n";
+        std::cout << e.what() << "\n";
+    }
+    catch (std::exception &e)
+    {
+        std::cout << "Exception, STOPPING PROGRAM from rank " << rank << "\n";
+        std::cout << e.what() << "\n";
+    }
+
+    // Add code to finalize MPI
+
+    return 0;
+}