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Chapters:
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<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
<a href="InvokingGri.html">3: Invocation</a><br>
<a href="GettingMoreControl.html">4: Finer Control</a><br>
<a href="X-Y.html">5: X-Y Plots</a><br>
<a href="ContourPlots.html">6: Contour Plots</a><br>
<a href="Images.html">7: Image Plots</a><br>
<a href="Examples.html">8: Examples</a><br>
<a href="Commands.html">9: Gri Commands</a><br>
<a href="Programming.html">10: Programming</a><br>
<a href="Environment.html">11: Environment</a><br>
<a href="Emacs.html">12: Emacs Mode</a><br>
<a href="History.html">13: History</a><br>
<a href="Installation.html">14: Installation</a><br>
<a href="Bugs.html">15: Gri Bugs</a><br>
<a href="TestSuite.html">16: Test Suite</a><br>
<a href="Acknowledgments.html">17: Acknowledgments</a><br>
<a href="License.html">18: License</a><br>
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Indices:</br>
<a href="ConceptIndex.html"><i>Concepts</i></a><br>
<a href="CommandIndex.html"><i>Commands</i></a><br>
<a href="BuiltinIndex.html"><i>Variables</i></a><br>
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<h2>10.15: Missing data</h2>
<!-- latex: \index{@code{..missingvalue..}, value for missing data} -->
Most Gri commands will ignore data points equal to a "missing value."
For example, `<font color="#82140F"><code>draw curve</code></font>' connects only points which are not equal
(to within 0.01 percent) of the missing value. The curve has holes at
missing data. Initially the missing-value is set to 1.0e22. You may
alter this value with `<font color="#82140F"><code>set missing value .value.</code></font>'.
The built-in variable `<font color="#82140F"><code>..missingvalue..</code></font>' stores the current value
of the missing-value.
<p>
Additionally, Gri will ignore anything it reads that is equal to the
string `<font color="#82140F"><code>NaN</code></font>' or `<font color="#82140F"><code>Inf</code></font>'. These are produced by matlab, C, and
other programs when dividing by zero, etc.
<p>
Gri also ignores mathematical operations on data items which are equal to
the missing value. Thus, for example, if your missing value is -99 then
the command `<font color="#82140F"><code>x += 1</code></font>' will not change the values equal to -99 to -98,
since this would have the side-effect of making the datum no longer be
considered missing.
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