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<!--Copyright (C) 1988-2005 by the Institute of Global Environment and Society (IGES). See file COPYRIGHT for more information.-->
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<title>GrADS Function: if</title>
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<H2><b>if()</b></H2>
<p>
This function performs an if/then/else expression evaluation.
It is available starting with <span class="red">GrADS version 2.1.1.b0</span>.
<h3>Syntax</h3>
<p>
<code>if (<i>logical_expr, then_expr, else_expr</i>)</code>
<p>
where:
<ul>
<p><code><i>logical_expr</i> </code>- any valid logical expression that has a boolean (yes/no) result<br>
<code><i>then_expr</i> </code>- the result expression if <code><i>logical_expr</i></code> is true<br>
<code><i>else_expr </i> </code>- the result expression if <code><i>logical_expr</i></code> is false<br>
</ul>
<p>All the arguments must be expressions for gridded data -- the logical operators and the if() function have not yet been implemented for station data. <br>
</p>
<H3>Usage Notes</H3>
<ol>
<li>The <code><i>logical_expr</i></code> should include one or more of the logical operators:<code> =, !=, >, >=, <, <=, |, &</code><br>
<br>
The result of a logical operation is boolean -- an answer to a yes/no question. If the expression is true the result is 1, and if the expression is false the answer is -1. The <code>if()</code> function will evaluate <code><i>logical_expr</i></code> and wherever the result is >0 it will place the value of <code><i>then_expr</i></code>, and wherever the result is <0 it will place the value of <code><i>else_expr</i></code>.<br>
<br>
<li>The arguments<code><i>then_expr</i></code> and <code><i>else_expr</i></code> may be any GrADS expression, including a constant. If you want <code><i>then_expr</i></code> or <code><i>else_expr</i></code> to be undefined, then use <code><a href="gradfuncmaskout.html">maskout()</a></code> instead of the <code><a href="gradfuncif.html">if()</a></code> function.
</ol>
<h3>Examples</h3>
<p>Here is a script sample to find the minimum and maximum 2-meter temperature at each grid point over a 12-month period:<dd><code>
'define tmin = const(t2m,1e9)'<br>
'define tmax = const(t2m,-1e9)'<br>
t = 1<br>
while (t <= 12) <br>
'set t 't<br>
'define tmin = if(t2m<tmin,t2m,tmin)'<br>
'define tmax = if(t2m>tmax,t2m,tmax)'<br>
t = t + 1<br>
endwhile
</code>
</dd>
</p>
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