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<div class="title">Writing by Chunk </div> </div>
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<div class="textblock"><p>Navigate back: <a class="el" href="index.html">Main</a> / <a class="el" href="_getting_started.html">Getting Started with HDF5</a> / <a class="el" href="_intro_par_h_d_f5.html">A Brief Introduction to Parallel HDF5</a> </p><hr />
<p>In this example each process writes a "chunk" of data to a dataset. The C and Fortran 90 examples result in the same data layout in the file.</p>
<table class="doxtable">
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<th><b>Figure a</b> C Example </th><th><b>Figure b</b> Fortran Example </th></tr>
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<p>For this example, four processes are used, and a 4 x 2 chunk is written to the dataset by each process.</p>
<p>To do this, you would: </p><ul>
<li>Use the block parameter to specify a chunk of size 4 x 2 (or 2 x 4 for Fortran). </li>
<li>Use a different offset (start) for each process, based on the chunk size: <table class="doxtable">
<tr>
<th rowspan="3"><b>C</b></th><th>Process 0</th><th>Process 1</th><th>Process 2</th><th>Process 3 </th></tr>
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<td>offset[0] = 0</td><td>offset[0] = 0</td><td>offset[0] = 4</td><td>offset[0] = 4 </td></tr>
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<td>offset[1] = 0</td><td>offset[1] = 2</td><td>offset[1] = 0</td><td>offset[1] = 2 </td></tr>
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<th rowspan="3"><b>Fortran</b></th><th>Process 0</th><th>Process 1</th><th>Process 2</th><th>Process 3 </th></tr>
<tr>
<td>offset(1) = 0</td><td>offset(1) = 2</td><td>offset(1) = 0</td><td>offset(1) = 2 </td></tr>
<tr>
<td>offset(2) = 0</td><td>offset(2) = 0</td><td>offset(2) = 4</td><td>offset(2) = 4 </td></tr>
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</li>
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<p>For example, the offset and block parameters for Process 2 would look like: </p><table class="doxtable">
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<th><b>Figure a</b> C Example </th><th><b>Figure b</b> Fortran Example </th></tr>
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<p>Below are example programs for writing hyperslabs by pattern in Parallel HDF5: </p><table class="doxtable">
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<td><a href="https://github.com/HDFGroup/hdf5-examples/blob/master/C/H5Parallel/ph5_hyperslab_by_chunk.c">hyperslab_by_chunk.c</a> </td></tr>
<tr>
<td><a href="https://github.com/HDFGroup/hdf5-examples/blob/master/Fortran/H5Parallel/ph5_f90_hyperslab_by_chunk.F90">hyperslab_by_chunk.F90</a> </td></tr>
</table>
<p>The following is the output from h5dump for the HDF5 file created in this example: </p><div class="fragment"><div class="line">HDF5 <span class="stringliteral">"SDS_chnk.h5"</span> {</div>
<div class="line">GROUP <span class="stringliteral">"/"</span> {</div>
<div class="line"> DATASET <span class="stringliteral">"IntArray"</span> {</div>
<div class="line"> DATATYPE <a class="code" href="group___p_d_t_s_t_d.html#ga37e8a6be7ee64587c2a282b965019bb8">H5T_STD_I32BE</a> </div>
<div class="line"> DATASPACE SIMPLE { ( 8, 4 ) / ( 8, 4 ) } </div>
<div class="line"> DATA {</div>
<div class="line"> 1, 1, 2, 2,</div>
<div class="line"> 1, 1, 2, 2,</div>
<div class="line"> 1, 1, 2, 2,</div>
<div class="line"> 1, 1, 2, 2,</div>
<div class="line"> 3, 3, 4, 4,</div>
<div class="line"> 3, 3, 4, 4,</div>
<div class="line"> 3, 3, 4, 4,</div>
<div class="line"> 3, 3, 4, 4</div>
<div class="line"> } </div>
<div class="line"> } </div>
<div class="line">} </div>
<div class="line">} </div>
<div class="ttc" id="agroup___p_d_t_s_t_d_html_ga37e8a6be7ee64587c2a282b965019bb8"><div class="ttname"><a href="group___p_d_t_s_t_d.html#ga37e8a6be7ee64587c2a282b965019bb8">H5T_STD_I32BE</a></div><div class="ttdeci">#define H5T_STD_I32BE</div><div class="ttdef"><b>Definition:</b> H5Tpublic.h:305</div></div>
</div><!-- fragment --><p> The h5dump utility is written in C so the output is in C order.</p>
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