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<div class="headertitle"><div class="title">Writing by Pattern </div></div>
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<div class="textblock"><p>Navigate back: <a class="el" href="index.html" title="notitle">Main</a> / <a class="el" href="_getting_started.html" title="Getting Started with HDF5">Getting Started with HDF5</a> / <a class="el" href="_intro_par_h_d_f5.html" title="A Brief Introduction to Parallel HDF5">A Brief Introduction to Parallel HDF5</a> </p><hr />
<p>This is another example of writing data into disconnected locations in a file. Each process writes data from the contiguous buffer into regularly scattered locations in the file.</p>
<p>Each process defines a hyperslab in the file as described below and writes data to it. The C and Fortran 90 examples below 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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<img src="ppatt_figa.gif" alt=""/>
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<p>The C and Fortran 90 examples use four processes to write the pattern shown above. Each process defines a hyperslab by: </p><ul>
<li>Specifying a stride of 2 for each dimension, which indicates that you wish to write to every other position along a dimension. </li>
<li>Specifying a different offset for each process: <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>
<tr>
<td>offset[0] = 0</td><td>offset[0] = 1</td><td>offset[0] = 0</td><td>offset[0] = 1</td></tr>
<tr>
<td>offset[1] = 0</td><td>offset[1] = 0</td><td>offset[1] = 1</td><td>offset[1] = 1</td></tr>
<tr>
<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) = 0</td><td>offset(1) = 1</td><td>offset(1) = 1</td></tr>
<tr>
<td>offset(2) = 0</td><td>offset(2) = 1</td><td>offset(2) = 0</td><td>offset(2) = 1</td></tr>
</table>
</li>
<li>Specifying the size of the slab to write. The count is the number of positions along a dimension to write to. If writing a 4 x 2 slab, then the count would be: <table class="doxtable">
<tr>
<th><b>C</b></th><th>Fortran</th></tr>
<tr>
<td>count[0] = 4</td><td>count(1) = 2</td></tr>
<tr>
<td>count[1] = 2</td><td>count(2) = 4</td></tr>
</table>
</li>
</ul>
<p>For example, the offset, count, and stride parameters for Process 2 would look like: </p><table class="doxtable">
<tr>
<th><b>Figure a</b> C Example</th><th><b>Figure b</b> Fortran Example</th></tr>
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<td><div class="image">
<img src="ppatt_figc.gif" alt=""/>
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</td><td><div class="image">
<img src="ppatt_figd.gif" alt=""/>
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</td></tr>
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<p>Below are example programs for writing hyperslabs by pattern in Parallel HDF5: </p><table class="doxtable">
<tr>
<td><a href="https://github.com/HDFGroup/hdf5/blob/develop/HDF5Examples/C/H5PAR/ph5_hyperslab_by_pattern.c">hyperslab_by_pattern.c</a> </td></tr>
<tr>
<td><a href="https://github.com/HDFGroup/hdf5/blob/develop/HDF5Examples/FORTRAN/H5PAR/ph5_f90_hyperslab_by_pattern.F90">hyperslab_by_pattern.F90</a> </td></tr>
</table>
<p>The following is the output from <a class="el" href="_h5_t_o_o_l__d_p__u_g.html#sec_cltools_h5dump" title="h5dump">h5dump</a> for the HDF5 file created in this example: </p><div class="fragment"><div class="line">HDF5 <span class="stringliteral">&quot;SDS_pat.h5&quot;</span> {</div>
<div class="line">GROUP <span class="stringliteral">&quot;/&quot;</span> {</div>
<div class="line"> DATASET <span class="stringliteral">&quot;IntArray&quot;</span> {</div>
<div class="line"> DATATYPE <a class="code hl_define" 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, 3, 1, 3,</div>
<div class="line"> 2, 4, 2, 4,</div>
<div class="line"> 1, 3, 1, 3,</div>
<div class="line"> 2, 4, 2, 4,</div>
<div class="line"> 1, 3, 1, 3,</div>
<div class="line"> 2, 4, 2, 4,</div>
<div class="line"> 1, 3, 1, 3,</div>
<div class="line"> 2, 4, 2, 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:466</div></div>
</div><!-- fragment --><p> The <a class="el" href="_h5_t_o_o_l__d_p__u_g.html#sec_cltools_h5dump" title="h5dump">h5dump</a> utility is written in C so the output is in C order.</p>
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<p> Navigate back: <a class="el" href="index.html" title="notitle">Main</a> / <a class="el" href="_getting_started.html" title="Getting Started with HDF5">Getting Started with HDF5</a> / <a class="el" href="_intro_par_h_d_f5.html" title="A Brief Introduction to Parallel HDF5">A Brief Introduction to Parallel HDF5</a> </p>
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