Hello, I downloaded Boost in order to use the expint function: http://www.boost.org/doc/libs/1_37_0/libs/math/doc/sf_and_dist/html/math_too... I copied the /boost folder into the /include folder in Visual C++ where the other library files (stdio.h, etc.) are kept. In the .cpp file for the program I wanted to use expint in, I inserted the following line, taken from the description: #include <boost/math/special_functions/expint.hpp> When compiling, Visual C++ appears to be able to open expint.hpp, but it doesn't recognize the function: error C3861: 'expint': identifier not found Is there something else I need to add to the .cpp file so that expint will be recognized? I am using Visual C++ 2010 Express. Thanks, Keith