Add documentation

Author: mborland

doc/math.qbk

@@ -339,6 +339,10 @@ and use the function's name as the link text.]
 [def __hermite [link math_toolkit.sf_poly.hermite hermite]]
 [def __cardinal_b_splines [link math_toolkit.sf_poly.cardinal_b_splines cardinal_b_splines]]
 
+[/logistic functions]
+[def __logit [link math_toolkit.logistic.logit logit]]
+[def __logistic_sigmoid [link math_toolkit.logistic.logistic_sigmoid logistic_sigmoid]]
+
 [/Misc]
 [def __expint [link math_toolkit.expint.expint_i expint]]
 [def __spherical_harmonic [link math_toolkit.sf_poly.sph_harm spherical_harmonic]]
@@ -666,6 +670,11 @@ and as a CD ISBN 0-9504833-2-X  978-0-9504833-2-0, Classification 519.2-dc22.
 [include sf/jacobi.qbk]
 [endsect] [/section:sf_poly Polynomials]
 
+[section:logistic Logistic Functions]
+[include sf/logit.qbk]
+[include sf/logistic_sigmoid.qbk]
+[endsect] [/section:logistic Logistic Functions]
+
 [section:bessel Bessel Functions]
 [include sf/bessel_introduction.qbk]
 [include sf/bessel_jy.qbk]

doc/sf/logistic_sigmoid.qbk

@@ -0,0 +1,30 @@
+[/
+  Copyright Matt Borland 2025
+  Distributed under the Boost Software License, Version 1.0.
+  (See accompanying file LICENSE_1_0.txt or copy at
+  http://www.boost.org/LICENSE_1_0.txt).
+]
+
+[section:logistic_sigmoid logistic_sigmoid]
+
+[h4 Synopsis]
+
+    #include <boost/math/special_functions/logistic_sigmoid.hpp>
+
+    namespace boost { namespace math {
+
+    template <typename RealType, typename Policy>
+    RealType logistic_sigmoid(RealType x, const Policy&);
+
+    template <typename RealType>
+    RealType logistic_sigmoid(RealType x)
+
+    }} // namespaces
+
+[h4 Description]
+
+Returns the [@https://en.wikipedia.org/wiki/Logistic_function logistic sigmoid function]
+This function is broadly useful, and is used to compute the CDF of the logistic distribution.
+It is also sometimes referred to as expit as it is the inverse of the logit function.
+
+[endsect]

doc/sf/logit.qbk

@@ -0,0 +1,30 @@
+[/
+  Copyright Matt Borland 2025
+  Distributed under the Boost Software License, Version 1.0.
+  (See accompanying file LICENSE_1_0.txt or copy at
+  http://www.boost.org/LICENSE_1_0.txt).
+]
+
+[section:logit logit]
+
+[h4 Synopsis]
+
+    #include <boost/math/special_functions/logit.hpp>
+
+    namespace boost { namespace math {
+
+    template <typename RealType, typename Policy>
+    RealType logit(RealType x, const Policy&);
+
+    template <typename RealType>
+    RealType logit(RealType x)
+
+    }} // namespaces
+
+[h4 Description]
+
+Returns the [@https://en.wikipedia.org/wiki/Logit logit function]
+This function is broadly useful, and is used to compute the Quantile of the logistic distribution.
+The inverse of this function is the logistic_sigmoid.
+
+[endsect]