<div dir="ltr">Thank you. That made a huge difference.<br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, 16 Aug 2020 at 15:24, John Maddock via Boost-users &lt;<a href="mailto:boost-users@lists.boost.org">boost-users@lists.boost.org</a>&gt; wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
On 16/08/2020 21:15, Anirban Pal via Boost-users wrote:<br>
&gt;<br>
&gt; Hello,<br>
&gt;<br>
&gt; I’m using the tanh-sinh integrator to integrate a simple function f(x) <br>
&gt; = 0.26*x from 3.0 to 4.0.<br>
&gt; The exact result is 0.91. With the integrator I’m getting a result <br>
&gt; accurate to only 10^-18 with cpp_bin_float_100 multiprecision.<br>
&gt;<br>
You have the double precision constant 0.26 in your code, and since this <br>
is an inexact binary value, everything that depends on that constant is <br>
inherently limited to double precision.  Try constructing it as Real(26) <br>
/ 100.<br>
<br>
<br>
&gt; |typedef boost::multiprecision::cpp_bin_float_100 Real; int main(int <br>
&gt; argc, char **argv) { using namespace boost::math::quadrature; using <br>
&gt; namespace std::placeholders; tanh_sinh&lt;Real&gt; integrator; auto f2 = <br>
&gt; [](Real x) { Real a = 0.26; return x*a; }; std::cout &lt;&lt; <br>
&gt; std::setprecision(std::numeric_limits&lt;Real&gt;::max_digits10) &lt;&lt; &quot;Comp.: <br>
&gt; &quot; &lt;&lt; integrator.integrate(f2, (Real) 3.0, (Real) 4.0) &lt;&lt; std::endl; <br>
&gt; return 0; } |<br>
&gt; I&#39;m getting an output of<br>
&gt;<br>
&gt; Comp.: <br>
&gt; 0.9100000000000000310862446895043831318616867065429687499999999999999999999999999999999999999999999999429<br>
&gt;<br>
&gt; which I&#39;m a bit curious about. I was wondering if I can improve the <br>
&gt; result.<br>
&gt;<br>
&gt; Thank you.<br>
&gt;<br>
&gt;<br>
&gt; -- <br>
&gt; Anirban Pal<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
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</blockquote></div><br clear="all"><br>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Anirban Pal</div><br></div></div></div></div></div></div></div></div><br><div><br></div></div></div></div></div></div></div></div></div></div></div>