ReadMe.md

examples/heatTransfer

This example solves a 2D Poisson equation for temperature in homogeneous media
using finite differences. This examples shows a straight-forward way to hook 
an application to the ADIOS2 library for its IO.


1. write: illustrates the Write API as well as has implementations of other IO libraries
  
    * adios 1.x    
    * hdf5 sequential, separate file per process per step
    * phdf5 parallel, steps appended to the same one file

2. read: illustrates the Read API that allows running the reader either as

    * post-mortem to read all output steps
    * in situ to read step by step as the writer outputs them 
       (need to run with a suitable engine)

3. read_fileonly: illustrates reading all output steps at once (a single read 
   statement) into a single contiguous memory block. This approach only works 
   for post-mortem processing. 



Example


1. Produce an output

Writer usage:  heatTransfer  config output  N  M   nx  ny   steps iterations
  config: XML config file to use
  output: name of output data file/stream
  N:      number of processes in X dimension
  M:      number of processes in Y dimension
  nx:     local array size in X dimension per processor
  ny:     local array size in Y dimension per processor
  steps:  the total number of steps to output
  iterations: one step consist of this many iterations

The ADIOS2 executable needs an XML config file to select the Engine used for the output. The engines are: BPFile, ADIOS1 and HDF5, the corresponding XML config files are in the examples/heatTransfer/ directory.

The adios1, ph5 and hdf5 versions of the example do not use XML config files, so just type "none" for the config argument.

$  mpirun -np 12 ./bin/heatTransfer_write_adios2 ../examples/heatTransfer/heat_bpfile.xml  heat  4 3  5 10 10 10


2. Read the output step-by-step and print data into text files (data.<rank> per reader process)

Reader Usage:   heatRead  config  input  N  M 
  config: XML config file to use
  input:  name of input data file/stream
  N:      number of processes in X dimension
  M:      number of processes in Y dimension


$ mpirun -np 2 ./bin/heatTransfer_read ../examples/heatTransfer/heat.xml heat 2 1 


Notes:
1. 	Engines for file-based output and post-mortem reading: i

   * BPFileWriter/BPFileReader
   * HDF5Writer/HDF5Reader
   * ADIOS1Writer/ADIOS1Reader

2. Engines for in situ execution

   * DataManWriter/DataManReader
     (Must run writer and reader with the same number of processes and same decomposition)