LAPACK is the best linear algebra library and it is free. Hence it would be just stupid not to use it. LAPACK Users’ Guide gives a good introduction in the library, so it is good to have it. The guide with the difference to the code does cost some money but this will be a pretty good investment. Well, if you are short on money, you can find the LAPACK guide on Netlib for free. Mathematicians are nice people, aren’t they?