to compute Bessel fct, prefer GSL over Boost

Sample/Interface/LayerRoughness.cpp

@@ -15,7 +15,7 @@
 #include "Sample/Interface/LayerRoughness.h"
 #include "Base/Py/PyFmt.h"
 #include "Base/Util/Assert.h"
-#include <boost/math/special_functions/bessel.hpp>
+#include <gsl/gsl_sf_bessel.h>
 #include <numbers>
 
 using std::numbers::pi;
@@ -73,7 +73,7 @@ double LayerRoughness::corrFunction(const R3 k) const
     double clength = m_lateral_corr_length;
     double R = sqrt(k.x() * k.x() + k.y() * k.y());
     return m_sigma * m_sigma * std::pow(2., 1 - H) / tgamma(H) * std::pow(R / clength, H)
-           * boost::math::cyl_bessel_k(H, R / clength);
+           * gsl_sf_bessel_Knu(H, R / clength);
 }
 
 std::string LayerRoughness::pythonConstructor() const