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<div class="chlinkprevnexttop"> <a href="chap0.html">[Top of Book]</a> <a href="chap0.html#contents">[Contents]</a> <a href="chap18.html">[Previous Chapter]</a> <a href="chap20.html">[Next Chapter]</a> </div>
<p id="mathjaxlink" class="pcenter"><a href="chap19_mj.html">[MathJax on]</a></p>
<p><a id="X81AA901181CA568F" name="X81AA901181CA568F"></a></p>
<div class="ChapSects"><a href="chap19.html#X81AA901181CA568F">19 <span class="Heading">Floats</span></a>
<div class="ContSect"><span class="tocline"><span class="nocss"> </span><a href="chap19.html#X7B4092CA7ABB93B0">19.1 <span class="Heading">A sample run</span></a>
</span>
</div>
<div class="ContSect"><span class="tocline"><span class="nocss"> </span><a href="chap19.html#X8606FDCE878850EF">19.2 <span class="Heading">Methods</span></a>
</span>
<div class="ContSSBlock">
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X87B6780178314628">19.2-1 <span class="Heading">Mathematical operations</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7BD96E0585D5A1EE">19.2-2 EqFloat</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7B3133497DDE839B">19.2-3 PrecisionFloat</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7D085DA987B0BDA6">19.2-4 <span class="Heading">Interval operations</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7DB3BC76836E6219">19.2-5 IsPInfinity</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X819050BF8403806E">19.2-6 FLOAT</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X873D56F67DD887C5">19.2-7 Float</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7BCD34DC7B5A0521">19.2-8 Rat</a></span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap19.html#X7A962B0983FA66E8">19.2-9 SetFloats</a></span>
</div></div>
<div class="ContSect"><span class="tocline"><span class="nocss"> </span><a href="chap19.html#X845ACF3A78BD2771">19.3 <span class="Heading">High-precision-specific methods</span></a>
</span>
</div>
<div class="ContSect"><span class="tocline"><span class="nocss"> </span><a href="chap19.html#X7E8F6EFB87A65F78">19.4 <span class="Heading">Complex arithmetic</span></a>
</span>
</div>
<div class="ContSect"><span class="tocline"><span class="nocss"> </span><a href="chap19.html#X7E57B09C80136484">19.5 <span class="Heading">Interval-specific methods</span></a>
</span>
</div>
</div>
<h3>19 <span class="Heading">Floats</span></h3>
<p>Starting with version 4.5, <strong class="pkg">GAP</strong> has built-in support for floating-point numbers in machine format, and allows package to implement arbitrary-precision floating-point arithmetic in a uniform manner. For now, one such package, <strong class="pkg">Float</strong> exists, and is based on the arbitrary-precision routines in <strong class="pkg">mpfr</strong>.</p>
<p>A word of caution: <strong class="pkg">GAP</strong> deals primarily with algebraic objects, which can be represented exactly in a computer. Numerical imprecision means that floating-point numbers do not form a ring in the strict <strong class="pkg">GAP</strong> sense, because addition is in general not associative (<code class="code">(1.0e-100+1.0)-1.0</code> is not the same as <code class="code">1.0e-100+(1.0-1.0)</code>, in the default precision setting).</p>
<p>Most algorithms in <strong class="pkg">GAP</strong> which require ring elements will therefore not be applicable to floating-point elements. In some cases, such a notion would not even make any sense (what is the greatest common divisor of two floating-point numbers?)</p>
<p><a id="X7B4092CA7ABB93B0" name="X7B4092CA7ABB93B0"></a></p>
<h4>19.1 <span class="Heading">A sample run</span></h4>
<p>Floating-point numbers can be input into <strong class="pkg">GAP</strong> in the standard floating-point notation:</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">3.14;</span>
3.14
<span class="GAPprompt">gap></span> <span class="GAPinput">last^2/6;</span>
1.64327
<span class="GAPprompt">gap></span> <span class="GAPinput">h := 6.62606896e-34;</span>
6.62607e-34
<span class="GAPprompt">gap></span> <span class="GAPinput">pi := 4*Atan(1.0);</span>
3.14159
<span class="GAPprompt">gap></span> <span class="GAPinput">hbar := h/(2*pi);</span>
1.05457e-34
</pre></div>
<p>Floating-point numbers can also be created using <code class="code">Float</code>, from strings or rational numbers; and can be converted back using <code class="code">String,Rat,Int</code>.</p>
<p><strong class="pkg">GAP</strong> allows rational and floating-point numbers to be mixed in the elementary operations <code class="code">+,-,*,/</code>. However, floating-point numbers and rational numbers may not be compared. Conversions are performed using the creator <code class="code">Float</code>:</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">Float("3.1416");</span>
3.1416
<span class="GAPprompt">gap></span> <span class="GAPinput">Float(355/113);</span>
3.14159
<span class="GAPprompt">gap></span> <span class="GAPinput">Rat(last);</span>
355/113
<span class="GAPprompt">gap></span> <span class="GAPinput">Rat(0.33333);</span>
1/3
<span class="GAPprompt">gap></span> <span class="GAPinput">Int(1.e10);</span>
10000000000
<span class="GAPprompt">gap></span> <span class="GAPinput">Int(1.e20);</span>
100000000000000000000
<span class="GAPprompt">gap></span> <span class="GAPinput">Int(1.e30);</span>
1000000000000000019884624838656
</pre></div>
<p><a id="X8606FDCE878850EF" name="X8606FDCE878850EF"></a></p>
<h4>19.2 <span class="Heading">Methods</span></h4>
<p>Floating-point numbers may be directly input, as in any usual mathematical software or language; with the exception that every floating-point number must contain a decimal digit. Therefore <code class="code">.1</code>, <code class="code">.1e1</code>, <code class="code">-.999</code> etc. are all valid <strong class="pkg">GAP</strong> inputs.</p>
<p>Floating-point numbers so entered in <strong class="pkg">GAP</strong> are stored as strings. They are converted to floating-point when they are first used. This means that, if the floating-point precision is increased, the constants are reevaluated to fit the new format.</p>
<p>Floating-point numbers may be followed by an underscore, as in <code class="code">1._</code>. This means that they are to be immediately converted to the current floating-point format. The underscore may be followed by a single letter, which specifies which format/precision to use. By default, <strong class="pkg">GAP</strong> has a single floating-point handler, with fixed (53 bits) precision, and its format specifier is <code class="code">'l'</code> as in <code class="code">1._l</code>. Higher-precision floating-point computations is available via external packages; <strong class="pkg">float</strong> for example.</p>
<p>A record, <code class="func">FLOAT</code> (<a href="chap19.html#X819050BF8403806E"><span class="RefLink">19.2-6</span></a>), contains all relevant constants for the current floating-point format; see its documentation for details. Typical fields are <code class="code">FLOAT.MANT_DIG=53</code>, the constant <code class="code">FLOAT.VIEW_DIG=6</code> specifying the number of digits to view, and <code class="code">FLOAT.PI</code> for the constant <span class="SimpleMath">π</span>. The constants have the same name as their C counterparts, except for the missing initial <code class="code">DBL_</code> or <code class="code">M_</code>.</p>
<p>Floating-point numbers may be created using the single function <code class="func">Float</code> (<a href="chap19.html#X873D56F67DD887C5"><span class="RefLink">19.2-7</span></a>), which accepts as arguments rational, string, or floating-point numbers. Floating-point numbers may also be created, in any floating-point representation, using <code class="func">NewFloat</code> (<a href="chap19.html#X873D56F67DD887C5"><span class="RefLink">19.2-7</span></a>) as in <code class="code">NewFloat(IsIEEE754FloatRep,355/113)</code>, by supplying the category filter of the desired new floating-point number; or using <code class="func">MakeFloat</code> (<a href="chap19.html#X873D56F67DD887C5"><span class="RefLink">19.2-7</span></a>) as in <code class="code">NewFloat(1.0,355/113)</code>, by supplying a sample floating-point number.</p>
<p>Floating-point numbers may also be converted to other <strong class="pkg">GAP</strong> formats using the usual commands <code class="func">Int</code> (<a href="chap14.html#X87CA734380B5F68C"><span class="RefLink">14.2-3</span></a>), <code class="func">Rat</code> (<a href="chap17.html#X7EB4C646806A2BDE"><span class="RefLink">17.2-6</span></a>), <code class="func">String</code> (<a href="chap27.html#X81FB5BE27903EC32"><span class="RefLink">27.6-6</span></a>).</p>
<p>Exact conversion to and from floating-point format may be done using external representations. The "external representation" of a floating-point number <code class="code">x</code> is a pair <code class="code">[m,e]</code> of integers, such that <code class="code">x=m*2^(-1+e-LogInt(AbsInt(m),2))</code>. Conversion to and from external representation is performed as usual using <code class="func">ExtRepOfObj</code> (<a href="chap79.html#X8542B32A8206118C"><span class="RefLink">79.16-1</span></a>) and <code class="func">ObjByExtRep</code> (<a href="chap79.html#X8542B32A8206118C"><span class="RefLink">79.16-1</span></a>):</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">ExtRepOfObj(3.14);</span>
[ 7070651414971679, 2 ]
<span class="GAPprompt">gap></span> <span class="GAPinput">ObjByExtRep(IEEE754FloatsFamily,last);</span>
3.14
</pre></div>
<p>Computations with floating-point numbers never raise any error. Division by zero is allowed, and produces a signed infinity. Illegal operations, such as <code class="code">0./0.</code>, produce <code class="keyw">NaN</code>'s (not-a-number); this is the only floating-point number <code class="code">x</code> such that <code class="code">not EqFloat(x+0.0,x)</code>.</p>
<p>The IEEE754 standard requires <code class="keyw">NaN</code> to be non-equal to itself. On the other hand, <strong class="pkg">GAP</strong> requires every object to be equal to itself. To respect the IEEE754 standard, the function <code class="func">EqFloat</code> (<a href="chap19.html#X7BD96E0585D5A1EE"><span class="RefLink">19.2-2</span></a>) should be used instead of <code class="code">=</code>.</p>
<p>The category a floating-point belongs to can be checked using the filters <code class="func">IsFinite</code> (<a href="chap30.html#X808A4061809A6E67"><span class="RefLink">30.4-2</span></a>), <code class="func">IsPInfinity</code> (<a href="chap19.html#X7DB3BC76836E6219"><span class="RefLink">19.2-5</span></a>), <code class="func">IsNInfinity</code> (<a href="chap19.html#X7DB3BC76836E6219"><span class="RefLink">19.2-5</span></a>), <code class="func">IsXInfinity</code> (<a href="chap19.html#X7DB3BC76836E6219"><span class="RefLink">19.2-5</span></a>), <code class="func">IsNaN</code> (<a href="chap19.html#X7DB3BC76836E6219"><span class="RefLink">19.2-5</span></a>).</p>
<p>Comparisons between floating-point numbers and rationals are explicitly forbidden. The rationale is that objects belonging to different families should in general not be comparable in <strong class="pkg">GAP</strong>. Floating-point numbers are also approximations of real numbers, and don't follow the same rules; consider for example, using the default <strong class="pkg">GAP</strong> implementation of floating-point numbers,</p>
<div class="example"><pre>
<span class="GAPprompt">gap></span> <span class="GAPinput">1.0/3.0 = Float(1/3);</span>
true
<span class="GAPprompt">gap></span> <span class="GAPinput">(1.0/3.0)^5 = Float((1/3)^5);</span>
false
</pre></div>
<p><a id="X87B6780178314628" name="X87B6780178314628"></a></p>
<h5>19.2-1 <span class="Heading">Mathematical operations</span></h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Cos</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sin</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ SinCos</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Tan</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sec</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Csc</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Cot</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Asin</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Acos</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Atan</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Atan2</code>( <var class="Arg">y</var>, <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Cosh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sinh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Tanh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sech</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Csch</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Coth</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Asinh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Acosh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Atanh</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Log</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Log2</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Log10</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Log1p</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Exp</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Exp2</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Exp10</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Expm1</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Cuberoot</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Square</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Hypothenuse</code>( <var class="Arg">x</var>, <var class="Arg">y</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Ceil</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Floor</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Round</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Trunc</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Frac</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ SignFloat</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Argument</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Erf</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Zeta</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Gamma</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ ComplexI</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Usual mathematical functions.</p>
<p><a id="X7BD96E0585D5A1EE" name="X7BD96E0585D5A1EE"></a></p>
<h5>19.2-2 EqFloat</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ EqFloat</code>( <var class="Arg">x</var>, <var class="Arg">y</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Returns: Whether the floateans <var class="Arg">x</var> and <var class="Arg">y</var> are equal</p>
<p>This function compares two floating-point numbers, and returns <code class="keyw">true</code> if they are equal, and <code class="keyw">false</code> otherwise; with the exception that <code class="keyw">NaN</code> is always considered to be different from itself.</p>
<p><a id="X7B3133497DDE839B" name="X7B3133497DDE839B"></a></p>
<h5>19.2-3 PrecisionFloat</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ PrecisionFloat</code>( <var class="Arg">x</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Returns: The precision of <var class="Arg">x</var></p>
<p>This function returns the precision, counted in number of binary digits, of the floating-point number <var class="Arg">x</var>.</p>
<p><a id="X7D085DA987B0BDA6" name="X7D085DA987B0BDA6"></a></p>
<h5>19.2-4 <span class="Heading">Interval operations</span></h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sup</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Inf</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Mid</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ AbsoluteDiameter</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ RelativeDiameter</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Overlaps</code>( <var class="Arg">interval1</var>, <var class="Arg">interval2</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsDisjoint</code>( <var class="Arg">interval1</var>, <var class="Arg">interval2</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IncreaseInterval</code>( <var class="Arg">interval</var>, <var class="Arg">delta</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ BlowupInterval</code>( <var class="Arg">interval</var>, <var class="Arg">ratio</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ BisectInterval</code>( <var class="Arg">interval</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Most are self-explanatory. <code class="code">BlowupInterval</code> returns an interval with same midpoint but relative diameter increased by <var class="Arg">ratio</var>; <code class="code">IncreaseInterval</code> returns an interval with same midpoint but absolute diameter increased by <var class="Arg">delta</var>; <code class="code">BisectInterval</code> returns a list of two intervals whose union equals <var class="Arg">interval</var>.</p>
<p><a id="X7DB3BC76836E6219" name="X7DB3BC76836E6219"></a></p>
<h5>19.2-5 IsPInfinity</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsPInfinity</code>( <var class="Arg">x</var> )</td><td class="tdright">( property )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsNInfinity</code>( <var class="Arg">x</var> )</td><td class="tdright">( property )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsXInfinity</code>( <var class="Arg">x</var> )</td><td class="tdright">( property )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsFinite</code>( <var class="Arg">x</var> )</td><td class="tdright">( property )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ IsNaN</code>( <var class="Arg">x</var> )</td><td class="tdright">( property )</td></tr></table></div>
<p>Returns <code class="keyw">true</code> if the floating-point number <var class="Arg">x</var> is respectively <span class="SimpleMath">+∞</span>, <span class="SimpleMath">-∞</span>, <span class="SimpleMath">±∞</span>, finite, or `not a number', such as the result of <code class="code">0.0/0.0</code>.</p>
<p><a id="X819050BF8403806E" name="X819050BF8403806E"></a></p>
<h5>19.2-6 FLOAT</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ FLOAT</code></td><td class="tdright">( global variable )</td></tr></table></div>
<p>This record contains useful floating-point constants:</p>
<dl>
<dt><strong class="Mark">DECIMAL_DIG</strong></dt>
<dd><p>Maximal number of useful digits;</p>
</dd>
<dt><strong class="Mark">DIG</strong></dt>
<dd><p>Number of significant digits;</p>
</dd>
<dt><strong class="Mark">VIEW_DIG</strong></dt>
<dd><p>Number of digits to print in short view;</p>
</dd>
<dt><strong class="Mark">EPSILON</strong></dt>
<dd><p>Smallest number such that <span class="SimpleMath">1≠1+ϵ</span>;</p>
</dd>
<dt><strong class="Mark">MANT_DIG</strong></dt>
<dd><p>Number of bits in the mantissa;</p>
</dd>
<dt><strong class="Mark">MAX</strong></dt>
<dd><p>Maximal representable number;</p>
</dd>
<dt><strong class="Mark">MAX_10_EXP</strong></dt>
<dd><p>Maximal decimal exponent;</p>
</dd>
<dt><strong class="Mark">MAX_EXP</strong></dt>
<dd><p>Maximal binary exponent;</p>
</dd>
<dt><strong class="Mark">MIN</strong></dt>
<dd><p>Minimal positive representable number;</p>
</dd>
<dt><strong class="Mark">MIN_10_EXP</strong></dt>
<dd><p>Minimal decimal exponent;</p>
</dd>
<dt><strong class="Mark">MIN_EXP</strong></dt>
<dd><p>Minimal exponent;</p>
</dd>
<dt><strong class="Mark">INFINITY</strong></dt>
<dd><p>Positive infinity;</p>
</dd>
<dt><strong class="Mark">NINFINITY</strong></dt>
<dd><p>Negative infinity;</p>
</dd>
<dt><strong class="Mark">NAN</strong></dt>
<dd><p>Not-a-number,</p>
</dd>
</dl>
<p>as well as mathematical constants <code class="code">E</code>, <code class="code">LOG2E</code>, <code class="code">LOG10E</code>, <code class="code">LN2</code>, <code class="code">LN10</code>, <code class="code">PI</code>, <code class="code">PI_2</code>, <code class="code">PI_4</code>, <code class="code">1_PI</code>, <code class="code">2_PI</code>, <code class="code">2_SQRTPI</code>, <code class="code">SQRT2</code>, <code class="code">SQRT1_2</code>.</p>
<p><a id="X873D56F67DD887C5" name="X873D56F67DD887C5"></a></p>
<h5>19.2-7 Float</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Float</code>( <var class="Arg">obj</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ NewFloat</code>( <var class="Arg">filter</var>, <var class="Arg">obj</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ MakeFloat</code>( <var class="Arg">sample</var>, <var class="Arg">obj</var>, <var class="Arg">obj</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Returns: A new floating-point number, based on <var class="Arg">obj</var></p>
<p>This function creates a new floating-point number.</p>
<p>If <var class="Arg">obj</var> is a rational number, the created number is created with sufficient precision so that the number can (usually) be converted back to the original number (see <code class="func">Rat</code> (<a href="../../doc/ref/chap17.html#X7EB4C646806A2BDE"><span class="RefLink">Reference: Rat</span></a>) and <code class="func">Rat</code> (<a href="chap17.html#X7EB4C646806A2BDE"><span class="RefLink">17.2-6</span></a>)). For an integer, the precision, if unspecified, is chosen sufficient so that <code class="code">Int(Float(obj))=obj</code> always holds, but at least 64 bits.</p>
<p><var class="Arg">obj</var> may also be a string, which may be of the form <code class="code">"3.14e0"</code> or <code class="code">".314e1"</code> or <code class="code">".314@1"</code> etc.</p>
<p>An option may be passed to specify, it bits, a desired precision. The format is <code class="code">Float("3.14":PrecisionFloat:=1000)</code> to create a 1000-bit approximation of <span class="SimpleMath">3.14</span>.</p>
<p>In particular, if <var class="Arg">obj</var> is already a floating-point number, then <code class="code">Float(obj:PrecisionFloat:=prec)</code> creates a copy of <var class="Arg">obj</var> with a new precision. prec</p>
<p><a id="X7BCD34DC7B5A0521" name="X7BCD34DC7B5A0521"></a></p>
<h5>19.2-8 Rat</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Rat</code>( <var class="Arg">f</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<p>Returns: A rational approximation to <var class="Arg">f</var></p>
<p>This command constructs a rational approximation to the floating-point number <var class="Arg">f</var>. Of course, it is not guaranteed to return the original rational number <var class="Arg">f</var> was created from, though it returns the most `reasonable' one given the precision of <var class="Arg">f</var>.</p>
<p>Two options control the precision of the rational approximation: In the form <code class="code">Rat(f:maxdenom:=md,maxpartial:=mp)</code>, the rational returned is such that the denominator is at most <var class="Arg">md</var> and the partials in its continued fraction expansion are at most <var class="Arg">mp</var>. The default values are <code class="code">maxpartial:=10000</code> and <code class="code">maxdenom:=2^(precision/2)</code>.</p>
<p><a id="X7A962B0983FA66E8" name="X7A962B0983FA66E8"></a></p>
<h5>19.2-9 SetFloats</h5>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ SetFloats</code>( <var class="Arg">rec</var>[, <var class="Arg">bits</var>][, <var class="Arg">install</var>] )</td><td class="tdright">( function )</td></tr></table></div>
<p>Installs a new interface to floating-point numbers in <strong class="pkg">GAP</strong>, optionally with a desired precision <var class="Arg">bits</var> in binary digits. The last optional argument <var class="Arg">install</var> is a boolean value; if false, it only installs the eager handler and the precision for the floateans, without making them the default.</p>
<p><a id="X845ACF3A78BD2771" name="X845ACF3A78BD2771"></a></p>
<h4>19.3 <span class="Heading">High-precision-specific methods</span></h4>
<p><strong class="pkg">GAP</strong> provides a mechanism for packages to implement new floating-point numerical interfaces. The following describes that mechanism, actual examples of packages are documented separately.</p>
<p>A package must create a record with fields (all optional)</p>
<dl>
<dt><strong class="Mark">creator</strong></dt>
<dd><p>a function converting strings to floating-point;</p>
</dd>
<dt><strong class="Mark">eager</strong></dt>
<dd><p>a character allowing immediate conversion to floating-point;</p>
</dd>
<dt><strong class="Mark">objbyextrep</strong></dt>
<dd><p>a function creating a floating-point number out of a list <code class="code">[mantissa,exponent]</code>;</p>
</dd>
<dt><strong class="Mark">filter</strong></dt>
<dd><p>a filter for the new floating-point objects;</p>
</dd>
<dt><strong class="Mark">constants</strong></dt>
<dd><p>a record containing numerical constants, such as <code class="code">MANT_DIG</code>, <code class="code">MAX</code>, <code class="code">MIN</code>, <code class="code">NAN</code>.</p>
</dd>
</dl>
<p>The package must install methods <code class="code">Int</code>, <code class="code">Rat</code>, <code class="code">String</code> for its objects, and creators <code class="code">NewFloat(filter,IsRat)</code>, <code class="code">NewFloat(IsString)</code>.</p>
<p>It must then install methods for all arithmetic and numerical operations: <code class="code">PLUS</code>, <code class="code">Exp</code>, ...</p>
<p>The user chooses that implementation by calling <code class="func">SetFloats</code> (<a href="chap19.html#X7A962B0983FA66E8"><span class="RefLink">19.2-9</span></a>) with the record as argument, and with an optional second argument requesting a precision in binary digits.</p>
<p><a id="X7E8F6EFB87A65F78" name="X7E8F6EFB87A65F78"></a></p>
<h4>19.4 <span class="Heading">Complex arithmetic</span></h4>
<p>Complex arithmetic may be implemented in packages, and is present in <strong class="pkg">float</strong>. Complex numbers are treated as usual numbers; they may be input with an extra "i" as in <code class="code">-0.5+0.866i</code>.</p>
<p>Methods should then be implemented for <code class="code">Norm</code>, <code class="code">RealPart</code>, <code class="code">ImaginaryPart</code>, <code class="code">ComplexConjugate</code>, ...</p>
<p><a id="X7E57B09C80136484" name="X7E57B09C80136484"></a></p>
<h4>19.5 <span class="Heading">Interval-specific methods</span></h4>
<p>Interval arithmetic may also be implemented in packages. Intervals are in fact efficient implementations of sets of real numbers. The only non-trivial issue is how they should be compared. The standard <code class="code">EQ</code> tests if the intervals are equal; however, it is usually more useful to know if intervals overlap, or are disjoint, or are contained in each other. The methods provided by the package should include <code class="code">Sup,Inf,Mid,DiameterOfInterval,Overlaps,IsSubset,IsDisjoint</code>.</p>
<p>Note the usual convention that intervals are compared as in <span class="SimpleMath">[a,b]le[c,d]</span> if and only if <span class="SimpleMath">ale c</span> and <span class="SimpleMath">ble d</span>.</p>
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