added tutorial and test

Author: pancetta

docs/source/tutorial/doc_step_7_C.rst

@@ -0,0 +1,12 @@
+Full code: `pySDC/tutorial/step_7/C_pySDC_with_PETSc.py <https://github.com/Parallel-in-Time/pySDC/blob/master/pySDC/tutorial/step_7/C_pySDC_with_PETSc.py>`_
+
+Results:
+
+1 processor in time, 1 processor in space
+.. literalinclude:: ../../../step_7_C_out_1x1.txt
+
+1 processor in time, 2 processors in space
+.. literalinclude:: ../../../step_7_C_out_1x2.txt
+
+2 processor in time, 2 processors in space
+.. literalinclude:: ../../../step_7_C_out_2x2.txt

pySDC/tests/test_tutorials/test_step_7.py

@@ -1,11 +1,55 @@
+import subprocess
+import os
+
 from pySDC.tutorial.step_7.A_visualize_residuals import main as main_A
 from pySDC.tutorial.step_7.B_multistep_SDC import main as main_B
 
-
 def test_A():
     main_A()
 
 def test_B():
     main_B()
 
+def test_C_1x1():
+    # Set python path once
+    my_env = os.environ.copy()
+    my_env['PYTHONPATH'] = '../../..:.'
+    cwd = '.'
+    num_procs = 1
+    num_procs_space = 1
+    cmd = ('mpirun -np ' + str(num_procs) + ' python pySDC/tutorial/step_7/C_pySDC_with_PETSc.py '
+           + str(num_procs_space) + ' ' + 'step_7_C_out_1x1.txt').split()
+    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=my_env, cwd=cwd)
+    p.wait()
+    assert p.returncode == 0, 'ERROR: did not get return code 0, got %s with %2i processes' % \
+                              (p.returncode, num_procs)
+
+def test_C_1x2():
+    # Set python path once
+    my_env = os.environ.copy()
+    my_env['PYTHONPATH'] = '../../..:.'
+    cwd = '.'
+    num_procs = 2
+    num_procs_space = 2
+    cmd = ('mpirun -np ' + str(num_procs) + ' python pySDC/tutorial/step_7/C_pySDC_with_PETSc.py '
+           + str(num_procs_space) + ' ' + 'step_7_C_out_1x2.txt').split()
+    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=my_env, cwd=cwd)
+    p.wait()
+    assert p.returncode == 0, 'ERROR: did not get return code 0, got %s with %2i processes' % \
+                              (p.returncode, num_procs)
+
+def test_C_2x2():
+    # Set python path once
+    my_env = os.environ.copy()
+    my_env['PYTHONPATH'] = '../../..:.'
+    cwd = '.'
+    num_procs = 4
+    num_procs_space = 2
+    cmd = ('mpirun -np ' + str(num_procs) + ' python pySDC/tutorial/step_7/C_pySDC_with_PETSc.py '
+           + str(num_procs_space) + ' ' + 'step_7_C_out_2x2.txt').split()
+    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=my_env, cwd=cwd)
+    p.wait()
+    assert p.returncode == 0, 'ERROR: did not get return code 0, got %s with %2i processes' % \
+                              (p.returncode, num_procs)
+
 

pySDC/tutorial/step_7/C_pySDC_with_PETSc.py

@@ -24,19 +24,20 @@ def main():
     world_size = comm.Get_size()
 
     # split world communicator to create space-communicators
-    if len(sys.argv) == 2:
+    if len(sys.argv) >= 2:
         color = int(world_rank / int(sys.argv[1]))
     else:
         color = int(world_rank / 1)
     space_comm = comm.Split(color=color)
     space_rank = space_comm.Get_rank()
 
     # split world communicator to create time-communicators
-    if len(sys.argv) == 2:
+    if len(sys.argv) >= 2:
         color = int(world_rank % int(sys.argv[1]))
     else:
         color = int(world_rank / world_size)
     time_comm = comm.Split(color=color)
+    time_rank = time_comm.Get_rank()
 
     # initialize level parameters
     level_params = dict()
@@ -113,9 +114,18 @@ def main():
     iter_counts = sort_stats(filtered_stats, sortby='time')
 
     niters = np.array([item[1] for item in iter_counts])
-    
+
+    # limit output to space-rank 0 (as before when setting the logger level)
     if space_rank == 0:
-        f = open('step_7_C_out.txt', 'w')
+        if len(sys.argv) == 3:
+            fname = str(sys.argv[2])
+        else:
+            fname = 'step_7_C_out.txt'
+        f = open(fname, 'a+')
+
+        out = 'This is time-rank %i...' % time_rank
+        f.write(out + '\n')
+        print(out)
 
         # compute and print statistics
         for item in iter_counts:

pySDC/tutorial/step_7/README.rst

@@ -33,6 +33,21 @@ Important things to note:
 
 .. include:: doc_step_7_B.rst
 
+Part C: Time-parallel pySDC with space-parallel PETSc
+-----------------------------------------------------
+
+With rather unfavorable scaling properties, parallel-in-time methods are only really useful when spatial parallelization is maxed out.
+To work with spatial parallelization, this part shows how to (1) include and work with an external library and (2) set up space- and time-parallel runs.
+We use again the forced heat equation as our testbed and PETSc for the space-parallel data structures and linear solver.
+See `implementations/datatype_classes/petsc_dmda_grid.py` and `implementations/problem_classes/HeatEquation_2D_PETSc_forced.py` for details on the PETSc bindings.
+
+Important things to note:
+
+- We need processors in space and time, which can be achieved by `comm.Split` and coloring. The space-communicator is then passed to the problem class.
+- Below we run the code 3 times: with 1 and 2 processors in space as well as 4 processors (2 in time and 2 in space). Do not expect scaling due to the CI environment.
+
+.. include:: doc_step_7_C.rst
+
 Part X: To be continued...
 --------------------------