The files
  inst/include/integration/GaussKronrodNodesWeights.h
  inst/include/integration/Integrator.h
were modified from library NumericalIntegration
(https://github.com/tbs1980/NumericalIntegration, MPL-2)
written by Sreekumar T. Balan, Matt Beall, and Mark Sauder.

The files
  inst/include/optimization/lbfgs.h
  src/arithmetic_ansi.h
  src/lbfgs.c
contained in RcppNumerical (< 0.3-0) were copied from the libLBFGS library
(https://www.chokkan.org/software/liblbfgs/, MIT)
written by Naoaki Okazaki.

The files
  inst/include/integration/cuba.h
  src/Cuhre.c
  src/cuhre/*
were modified from the Cuba library
(https://feynarts.de/cuba/, LGPL-3)
written by Thomas Hahn.

The code for 1-D numerical integration with infinite limits was contributed by
Ralf Stubner <ralf.stubner@gmail.com>.

Other part of this package was written by Yixuan Qiu.
