The code listings are copyrighted and commercially licensed by the "Numerical Recipes" authors. However, "Numerical Recipes" includes the following statement regarding copyrights on computer programs:Copyright does not protect ideas, but only the expression of those ideas in a particular form. In the case of a computer program, the ideas consist of the program's methodology and algorithm, including the necessary sequence of steps adopted by the programmer. The expression of those ideas is the program source code... If you analyze the ideas contained in a program, and then express those ideas in your own completely different implementation, then that new program implementation belongs to you.