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19<h4 style="line-height: 100%;"><font size="4">4.5.6 Plots of compressed
203d volume data with AVS</font></h4>
21<p style="line-height: 100%;">Files containing 3d volume data usually
22need large amounts of disc space. For parallel runs, the disc space
23requirement can
24be clearly reduced if the data are output in compressed format (note:
25currently a data
26compression is permitted only for parallel runs on Cray-T3E). Data
27compression
28can switched on by setting the initialization parameter <a
29 href="chapter_4.2.html#do3d_compress">do3d_compress</a>
30= <i>.TRUE.</i> and by assigning the desired accuracy (number of
31significant digits) via <a href="chapter_4.2.html#do3d_precision">do3d_precision</a>.
32A separate accuracy must be assigned for each individual quantity.
33Using uncompressed data, each grid point value is
34represented by a 32-bit real number, in case of compression the grid
35point values are represented by integers whose length depends
36on the desired accuracy (in general clearly smaller than 32 bits).
37The individual grid point values are packed into 32-bit integers and
38output. To plot these compressed data the following output command must
39be inserted into the
40<span style="font-weight: bold;">mrun</span> configuration file<b> </b>(in
41addition to the steps described
42in <a href="chapter_4.5.5.html">chapter
434.5.5</a>): </p>
44<ul>
45  <pre style="margin-bottom: 0.5cm; line-height: 100%;"><font
46 style="font-size: 10pt;" size="2">OC:[[ -f PLOT3D_COMPRESSED ]] &amp;&amp; tar cf PLOT3D_DATA PLOT3D_DATA_*</font></pre>
47</ul>
48<p style="line-height: 100%;">If a file named <tt><font
49 style="font-size: 10pt;" size="2">PLOT3D_COMPRESSED</font></tt>
50exists in the local working directory, <tt><font
51 face="Thorndale, serif">t</font></tt><font face="Thorndale, serif">he
52files produ</font>ced by the individual processors are packed into one
53file (<tt><font style="font-size: 10pt;" size="2">PLOT3D_DATA</font></tt>)
54using the "tar"
55command. The flag file
56<tt><font size="2">PLOT3D_COMPRESSED </font></tt>is created by PALM
57whenever data in compressed form is to be output. For
58uncompressed output, the individual files have to be joined via the
59program <tt><font style="font-size: 10pt;" size="2">combine_plot_fields.x</font>
60</tt>. In this case, an additional output command is also necessary
61(see chapter 4.5.5). For compressed output, this output command may
62remain
63unchanged in the configuration file, since <tt><font
64 style="font-size: 10pt;" size="2">combine_plot_fields.x</font></tt>
65recognizes the
66ex<font face="Thorndale, serif">isten</font>ce of <tt><font
67 style="font-size: 10pt;" size="2">PLOT3D_COMPRESSED</font></tt>
68and carries out no actions in such cases. </p>
69<p style="line-height: 100%;">The file connection statements for the
70local file <a href="chapter_3.4.html#PLOT3D_DATA">PLOT3D_DATA</a>
71and all further necessary statements to create plots of 3d volume
72data can be found in <a href="chapter_4.5.5.html">chapter
734.5.5</a>. </p>
74<p style="line-height: 100%;">After been transferred to the local
75computer
76of the user, the tar file with the compressed data cannot be read
77with the usual <span style="font-weight: bold;">AVS</span> module
78“read field”. Alternatively,
79the module “read_compressed_field” particularly developed
80for this purpose must be used. This module is located in a module
81library under: </p>
82<pre style="margin-bottom: 0.5cm; line-height: 100%;"><font
83 style="font-size: 10pt;" size="2">http://www.muk.uni-hannover.de/~raasch/PALM_group/AVS/Libraries/palm</font></pre>
84<p style="line-height: 100%;">This module must be loaded within AVS
85(network editor - &gt; module
86tools - &gt; read module library) and then it can be used like all
87other modules. <a
88 href="http://www.muk.uni-hannover.de/institut/people/raasch/PALM_group/AVS/Doc/read_compressed_field.html">Further
89information</a> about using this module is available (e.g. for
90accelerated treatment of compressed data with <span
91 style="font-weight: bold;">AVS</span> the module
92<a
93 href="http://www.muk.uni-hannover.de/institut/people/raasch/PALM_group/AVS/Doc/write_compressed_field.html">write_compressed_field</a>
94is available). <br>
95&nbsp; <br>
96&nbsp; </p>
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106<p style="line-height: 100%;">&nbsp;<i>Last change:&nbsp;</i> 20/04/05
107(SR)</p>
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