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|  | <html> | ||
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|  | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | ||
|  | <title>FAQs</title> | ||
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|  | <table cellpadding="2" width="100%"><tr> | ||
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|  | <div class="section"> | ||
|  | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | ||
|  | <a name="math_toolkit.constants_faq"></a><a class="link" href="constants_faq.html" title="FAQs">FAQs</a> | ||
|  | </h2></div></div></div> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h0"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.why_are_these_constants_chosen"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.why_are_these_constants_chosen">Why are | ||
|  |       <span class="emphasis"><em>these</em></span> Constants Chosen?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       It is, of course, impossible to please everyone with a list like this. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       Some of the criteria we have used are: | ||
|  |     </p> | ||
|  | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | ||
|  | <li class="listitem"> | ||
|  |           Used in Boost.Math. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Commonly used. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Expensive to compute. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Requested by users. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           <a href="http://en.wikipedia.org/wiki/Mathematical_constant" target="_top">Used in | ||
|  |           science and mathematics.</a> | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           No integer values (because so cheap to construct).<br> (You can easily | ||
|  |           define your own if found convenient, for example: <code class="computeroutput"><span class="identifier">FPT</span> | ||
|  |           <span class="identifier">one</span> <span class="special">=</span><span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">FPT</span><span class="special">>(</span><span class="number">42</span><span class="special">);</span></code>). | ||
|  |         </li> | ||
|  | </ul></div> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h1"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.how_are_constants_named"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.how_are_constants_named">How | ||
|  |       are constants named?</a> | ||
|  |     </h5> | ||
|  | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | ||
|  | <li class="listitem"> | ||
|  |           Not macros, so no upper case. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           All lower case (following C++ standard names). | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           No CamelCase. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Underscore as _ delimiter between words. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Numbers spelt as words rather than decimal digits (except following pow). | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Abbreviation conventions: | ||
|  |           <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> | ||
|  | <li class="listitem"> | ||
|  |                 root for square root. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 cbrt for cube root. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 pow for pow function using decimal digits like pow23 for n<sup>2/3</sup>. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 div for divided by or operator /. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 minus for operator -, plus for operator +. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 sqr for squared. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 cubed for cubed n<sup>3</sup>. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 words for greek, like π, ζ and Γ. | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 words like half, third, three_quarters, sixth for fractions. (Digit(s) | ||
|  |                 can get muddled). | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 log10 for log<sub>10</sub> | ||
|  |               </li> | ||
|  | <li class="listitem"> | ||
|  |                 ln for log<sub>e</sub> | ||
|  |               </li> | ||
|  | </ul></div> | ||
|  |         </li> | ||
|  | </ul></div> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h2"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.how_are_the_constants_derived"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.how_are_the_constants_derived">How are | ||
|  |       the constants derived?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       The constants have all been calculated using high-precision software working | ||
|  |       with up to 300-bit precision giving about 100 decimal digits. (The precision | ||
|  |       can be arbitrarily chosen and is limited only by compute time). | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h3"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.how_accurate_are_the_constants"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.how_accurate_are_the_constants">How Accurate | ||
|  |       are the constants?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       The minimum accuracy chosen (100 decimal digits) exceeds the accuracy of reasonably-foreseeable | ||
|  |       floating-point hardware (256-bit) and should meet most high-precision computations. | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h4"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.how_are_the_constants_tested"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.how_are_the_constants_tested">How are the | ||
|  |       constants tested?</a> | ||
|  |     </h5> | ||
|  | <div class="orderedlist"><ol class="orderedlist" type="1"> | ||
|  | <li class="listitem"> | ||
|  |           Comparison using Boost.Test BOOST_CHECK_CLOSE_FRACTION using long double | ||
|  |           literals, with at least 35 decimal digits, enough to be accurate for all | ||
|  |           long double implementations. The tolerance is usually twice <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span> <span class="identifier">epsilon</span></code>. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Comparison with calculation at long double precision. This often requires | ||
|  |           a slightly higher tolerance than two epsilon because of computational noise | ||
|  |           from round-off etc, especially when trig and other functions are called. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Comparison with independent published values, for example, using <a href="http://oeis.org/" target="_top">The On-Line Encyclopedia of Integer Sequences (OEIS)</a> | ||
|  |           again using at least 35 decimal digits strings. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Comparison with independely calculated values using arbitrary precision | ||
|  |           tools like <a href="http://www.wolfram.com/mathematica/" target="_top">Mathematica</a>, | ||
|  |           again using at least 35 decimal digits literal strings. | ||
|  |         </li> | ||
|  | </ol></div> | ||
|  | <div class="warning"><table border="0" summary="Warning"> | ||
|  | <tr> | ||
|  | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> | ||
|  | <th align="left">Warning</th> | ||
|  | </tr> | ||
|  | <tr><td align="left" valign="top"><p> | ||
|  |         We have not yet been able to <span class="bold"><strong>check</strong></span> that | ||
|  |         <span class="bold"><strong>all</strong></span> constants are accurate at the full arbitrary | ||
|  |         precision, at present 100 decimal digits. But certain key values like <code class="computeroutput"><span class="identifier">e</span></code> and <code class="computeroutput"><span class="identifier">pi</span></code> | ||
|  |         appear to be accurate and internal consistencies suggest that others are | ||
|  |         this accurate too. | ||
|  |       </p></td></tr> | ||
|  | </table></div> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h5"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.why_is_portability_important"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.why_is_portability_important">Why is Portability | ||
|  |       important?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       Code written using math constants is easily portable even when using different | ||
|  |       floating-point types with differing precision. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       It is a mistake to expect that results of computations will be <span class="bold"><strong>identical</strong></span>, | ||
|  |       but you can achieve the <span class="bold"><strong>best accuracy possible for the | ||
|  |       floating-point type in use</strong></span>. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       This has no extra cost to the user, but reduces irritating, and often confusing | ||
|  |       and very hard-to-trace effects, caused by the intrinsically limited precision | ||
|  |       of floating-point calculations. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       A harmless symptom of this limit is a spurious least-significant digit; at | ||
|  |       worst, slightly inaccurate constants sometimes cause iterating algorithms to | ||
|  |       diverge wildly because internal comparisons just fail. | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h6"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.what_is_the_internal_format_of_t"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.what_is_the_internal_format_of_t">What | ||
|  |       is the Internal Format of the constants, and why?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       See <a class="link" href="tutorial.html" title="Tutorial">tutorial</a> above for normal | ||
|  |       use, but this FAQ explains the internal details used for the constants. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       Constants are stored as 100 decimal digit values. However, some compilers do | ||
|  |       not accept decimal digits strings as long as this. So the constant is split | ||
|  |       into two parts, with the first containing at least 128-bit long double precision | ||
|  |       (35 decimal digits), and for consistency should be in scientific format with | ||
|  |       a signed exponent. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       The second part is the value of the constant expressed as a string literal, | ||
|  |       accurate to at least 100 decimal digits (in practice that means at least 102 | ||
|  |       digits). Again for consistency use scientific format with a signed exponent. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       For types with precision greater than a long double, then if T is constructible | ||
|  |       <code class="computeroutput"><span class="identifier">T</span> </code>is constructible from a | ||
|  |       <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span></code> then it's directly constructed from the string, | ||
|  |       otherwise we fall back on lexical_cast to convert to type <code class="computeroutput"><span class="identifier">T</span></code>. | ||
|  |       (Using a string is necessary because you can't use a numeric constant since | ||
|  |       even a <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span></code> | ||
|  |       might not have enough digits). | ||
|  |     </p> | ||
|  | <p> | ||
|  |       So, for example, a constant like pi is internally defined as | ||
|  |     </p> | ||
|  | <pre class="programlisting"><span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">pi</span><span class="special">,</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">,</span> <span class="string">"3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651e+00"</span><span class="special">);</span> | ||
|  | </pre> | ||
|  | <p> | ||
|  |       In this case the significand is 109 decimal digits, ensuring 100 decimal digits | ||
|  |       are exact, and exponent is zero. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       See <a class="link" href="new_const.html" title="Defining New Constants">defining new constants</a> to | ||
|  |       calculate new constants. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       A macro definition like this can be pasted into user code where convenient, | ||
|  |       or into <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code> if it | ||
|  |       is to be added to the Boost.Math library. | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h7"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.what_floating_point_types_could_"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.what_floating_point_types_could_">What | ||
|  |       Floating-point Types could I use?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       Apart from the built-in floating-point types <code class="computeroutput"><span class="keyword">float</span></code>, | ||
|  |       <code class="computeroutput"><span class="keyword">double</span></code>, <code class="computeroutput"><span class="keyword">long</span> | ||
|  |       <span class="keyword">double</span></code>, there are several arbitrary | ||
|  |       precision floating-point classes available, but most are not licensed for commercial | ||
|  |       use. | ||
|  |     </p> | ||
|  | <h6> | ||
|  | <a name="math_toolkit.constants_faq.h8"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.boost_multiprecision_by_christop"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.boost_multiprecision_by_christop">Boost.Multiprecision | ||
|  |       by Christopher Kormanyos</a> | ||
|  |     </h6> | ||
|  | <p> | ||
|  |       This work is based on an earlier work called e-float: Algorithm 910: A Portable | ||
|  |       C++ Multiple-Precision System for Special-Function Calculations, in ACM TOMS, | ||
|  |       {VOL 37, ISSUE 4, (February 2011)} (C) ACM, 2011. <a href="http://doi.acm.org/10.1145/1916461.1916469" target="_top">http://doi.acm.org/10.1145/1916461.1916469</a> | ||
|  |       <a href="https://svn.boost.org/svn/boost/sandbox/e_float/" target="_top">e_float</a> | ||
|  |       but is now re-factored and available under the Boost license in the Boost-sandbox | ||
|  |       at <a href="https://svn.boost.org/svn/boost/sandbox/multiprecision/" target="_top">multiprecision</a> | ||
|  |       where it is being refined and prepared for review. | ||
|  |     </p> | ||
|  | <h6> | ||
|  | <a name="math_toolkit.constants_faq.h9"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.boost_cpp_float_by_john_maddock_"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.boost_cpp_float_by_john_maddock_">Boost.cpp_float | ||
|  |       by John Maddock using Expression Templates</a> | ||
|  |     </h6> | ||
|  | <p> | ||
|  |       <a href="https://svn.boost.org/svn/boost/sandbox/big_number/" target="_top">Big Number</a> | ||
|  |       which is a reworking of <a href="https://svn.boost.org/svn/boost/sandbox/e_float/" target="_top">e_float</a> | ||
|  |       by Christopher Kormanyos to use expression templates for faster execution. | ||
|  |     </p> | ||
|  | <h6> | ||
|  | <a name="math_toolkit.constants_faq.h10"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.ntl_class_quad_float"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.ntl_class_quad_float">NTL | ||
|  |       class quad_float</a> | ||
|  |     </h6> | ||
|  | <p> | ||
|  |       <a href="http://shoup.net/ntl/" target="_top">NTL</a> by Victor Shoup has fixed and | ||
|  |       arbitrary high precision fixed and floating-point types. However none of these | ||
|  |       are licenced for commercial use. | ||
|  |     </p> | ||
|  | <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">NTL</span><span class="special">/</span><span class="identifier">quad_float</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> <span class="comment">// quad precision 106-bit, about 32 decimal digits.</span> | ||
|  | <span class="keyword">using</span> <span class="identifier">NTL</span><span class="special">::</span><span class="identifier">to_quad_float</span><span class="special">;</span> <span class="comment">// Less precise than arbitrary precision NTL::RR.</span> | ||
|  | </pre> | ||
|  | <p> | ||
|  |       NTL class <code class="computeroutput"><span class="identifier">quad_float</span></code>, which | ||
|  |       gives a form of quadruple precision, 106-bit significand (but without an extended | ||
|  |       exponent range.) With an IEC559/IEEE 754 compatible processor, for example | ||
|  |       Intel X86 family, with 64-bit double, and 53-bit significand, using the significands | ||
|  |       of <span class="bold"><strong>two</strong></span> 64-bit doubles, if <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="keyword">double</span><span class="special">>::</span><span class="identifier">digits10</span></code> is 16, then we get about twice the | ||
|  |       precision, so <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">quad_float</span><span class="special">>::</span><span class="identifier">digits10</span><span class="special">()</span></code> | ||
|  |       should be 32. (the default <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">RR</span><span class="special">>::</span><span class="identifier">digits10</span><span class="special">()</span></code> | ||
|  |       should be about 40). (which seems to agree with experiments). We output constants | ||
|  |       (including some noisy bits, an approximation to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">RR</span><span class="special">>::</span><span class="identifier">max_digits10</span><span class="special">()</span></code>) | ||
|  |       by adding 2 or 3 extra decimal digits, so using <code class="computeroutput"><span class="identifier">quad_float</span><span class="special">::</span><span class="identifier">SetOutputPrecision</span><span class="special">(</span><span class="number">32</span> <span class="special">+</span> | ||
|  |       <span class="number">3</span><span class="special">);</span></code> | ||
|  |     </p> | ||
|  | <p> | ||
|  |       Apple Mac/Darwin uses a similar <span class="emphasis"><em>doubledouble</em></span> 106-bit for | ||
|  |       its built-in <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span></code> | ||
|  |       type. | ||
|  |     </p> | ||
|  | <div class="note"><table border="0" summary="Note"> | ||
|  | <tr> | ||
|  | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> | ||
|  | <th align="left">Note</th> | ||
|  | </tr> | ||
|  | <tr><td align="left" valign="top"><p> | ||
|  |         The precision of all <code class="computeroutput"><span class="identifier">doubledouble</span></code> | ||
|  |         floating-point types is rather odd and values given are only approximate. | ||
|  |       </p></td></tr> | ||
|  | </table></div> | ||
|  | <p> | ||
|  |       <span class="bold"><strong>New projects should use <a href="../../../../../libs/multiprecision/doc/html/index.html" target="_top">Boost.Multiprecision</a>.</strong></span> | ||
|  |     </p> | ||
|  | <h6> | ||
|  | <a name="math_toolkit.constants_faq.h11"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.ntl_class_rr"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.ntl_class_rr">NTL | ||
|  |       class RR</a> | ||
|  |     </h6> | ||
|  | <p> | ||
|  |       Arbitrary precision floating point with NTL class RR, default is 150 bit (about | ||
|  |       50 decimal digits) used here with 300 bit to output 100 decimal digits, enough | ||
|  |       for many practical non-'number-theoretic' C++ applications. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       <a href="http://www.shoup.net/ntl/" target="_top">NTL A Library for doing Number Theory</a> | ||
|  |       is <span class="bold"><strong>not licenced for commercial use</strong></span>. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       This class is used in Boost.Math and is an option when using big_number projects | ||
|  |       to calculate new math constants. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       <span class="bold"><strong>New projects should use <a href="../../../../../libs/multiprecision/doc/html/index.html" target="_top">Boost.Multiprecision</a>.</strong></span> | ||
|  |     </p> | ||
|  | <h6> | ||
|  | <a name="math_toolkit.constants_faq.h12"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.gmp_and_mpfr"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.gmp_and_mpfr">GMP | ||
|  |       and MPFR</a> | ||
|  |     </h6> | ||
|  | <p> | ||
|  |       <a href="http://gmplib.org" target="_top">GMP</a> and <a href="http://www.mpfr.org/" target="_top">MPFR</a> | ||
|  |       have also been used to compute constants, but are licensed under the <a href="http://www.gnu.org/copyleft/lesser.html" target="_top">Lesser GPL license</a> and | ||
|  |       are <span class="bold"><strong>not licensed for commercial use</strong></span>. | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h13"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.what_happened_to_a_previous_coll"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.what_happened_to_a_previous_coll">What | ||
|  |       happened to a previous collection of constants proposed for Boost?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       A review concluded that the way in which the constants were presented did not | ||
|  |       meet many peoples needs. None of the methods proposed met many users' essential | ||
|  |       requirement to allow writing simply <code class="computeroutput"><span class="identifier">pi</span></code> | ||
|  |       rather than <code class="computeroutput"><span class="identifier">pi</span><span class="special">()</span></code>. | ||
|  |       Many science and engineering equations look difficult to read when because | ||
|  |       function call brackets can be confused with the many other brackets often needed. | ||
|  |       All the methods then proposed of avoiding the brackets failed to meet all needs, | ||
|  |       often on grounds of complexity and lack of applicability to various realistic | ||
|  |       scenarios. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       So the simple namespace method, proposed on its own, but rejected at the first | ||
|  |       review, has been added to allow users to have convenient access to float, double | ||
|  |       and long double values, but combined with template struct and functions to | ||
|  |       allow simultaneous use with other non-built-in floating-point types. | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h14"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.why_do_the_constants_internally_"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.why_do_the_constants_internally_">Why do | ||
|  |       the constants (internally) have a struct rather than a simple function?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       A function mechanism was provided by in previous versions of Boost.Math. | ||
|  |     </p> | ||
|  | <p> | ||
|  |       The new mechanism is to permit partial specialization. See Custom Specializing | ||
|  |       a constant above. It should also allow use with other packages like <a href="http://www.ttmath.org/" target="_top">ttmath Bignum C++ library.</a> | ||
|  |     </p> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h15"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.where_can_i_find_other_high_prec"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.where_can_i_find_other_high_prec">Where | ||
|  |       can I find other high precision constants?</a> | ||
|  |     </h5> | ||
|  | <div class="orderedlist"><ol class="orderedlist" type="1"> | ||
|  | <li class="listitem"> | ||
|  |           Constants with very high precision and good accuracy (>40 decimal digits) | ||
|  |           from Simon Plouffe's web based collection <a href="http://pi.lacim.uqam.ca/eng/" target="_top">http://pi.lacim.uqam.ca/eng/</a>. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           <a href="https://oeis.org/" target="_top">The On-Line Encyclopedia of Integer Sequences | ||
|  |           (OEIS)</a> | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Checks using printed text optically scanned values and converted from: | ||
|  |           D. E. Knuth, Art of Computer Programming, Appendix A, Table 1, Vol 1, ISBN | ||
|  |           0 201 89683 4 (1997) | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           M. Abrahamovitz & I. E. Stegun, National Bureau of Standards, Handbook | ||
|  |           of Mathematical Functions, a reference source for formulae now superceded | ||
|  |           by | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Frank W. Olver, Daniel W. Lozier, Ronald F. Boisvert, Charles W. Clark, | ||
|  |           NIST Handbook of Mathemetical Functions, Cambridge University Press, ISBN | ||
|  |           978-0-521-14063-8, 2010. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           John F Hart, Computer Approximations, Kreiger (1978) ISBN 0 88275 642 7. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Some values from Cephes Mathematical Library, Stephen L. Moshier and CALC100 | ||
|  |           100 decimal digit Complex Variable Calculator Program, a DOS utility. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Xavier Gourdon, Pascal Sebah, 50 decimal digits constants at <a href="http://numbers.computation.free.fr/Constants/constants.html" target="_top">Number, | ||
|  |           constants and computation</a>. | ||
|  |         </li> | ||
|  | </ol></div> | ||
|  | <h5> | ||
|  | <a name="math_toolkit.constants_faq.h16"></a> | ||
|  |       <span class="phrase"><a name="math_toolkit.constants_faq.where_are_physical_constants"></a></span><a class="link" href="constants_faq.html#math_toolkit.constants_faq.where_are_physical_constants">Where are | ||
|  |       Physical Constants?</a> | ||
|  |     </h5> | ||
|  | <p> | ||
|  |       Not here in this Boost.Math collection, because physical constants: | ||
|  |     </p> | ||
|  | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | ||
|  | <li class="listitem"> | ||
|  |           Are measurements, not truely constants. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Are not truly constant and keeping changing as mensuration technology improves. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Have a instrinsic uncertainty. | ||
|  |         </li> | ||
|  | <li class="listitem"> | ||
|  |           Mathematical constants are stored and represented at varying precision, | ||
|  |           but should never be inaccurate. | ||
|  |         </li> | ||
|  | </ul></div> | ||
|  | <p> | ||
|  |       Some physical constants may be available in Boost.Units. | ||
|  |     </p> | ||
|  | </div> | ||
|  | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | ||
|  | <td align="left"></td> | ||
|  | <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, | ||
|  |       Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | ||
|  |       Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani, | ||
|  |       Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | ||
|  |         Distributed under the Boost Software License, Version 1.0. (See accompanying | ||
|  |         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | ||
|  |       </p> | ||
|  | </div></td> | ||
|  | </tr></table> | ||
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