GNU libmatheval
Introduction
GNU libmatheval is a library (callable from C and Fortran) to parse and evaluate symbolic expressions input as text. It supports expressions in any number of variables of arbitrary names, decimal and symbolic constants, basic unary and binary operators, and elementary mathematical functions. In addition to parsing and evaluation, libmatheval can also compute symbolic derivatives and output expressions to strings.
Downloading
GNU libmatheval can be found on http://ftp.gnu.org/gnu/libmatheval/ (via HTTP) and ftp://ftp.gnu.org/gnu/libmatheval/ (via FTP). It can also be found on one of GNU FTP mirrors.
GNU libmatheval development sources from Git repository are available for browsing through corresponding Savannah Web interface. Sources could be also fetched from repository by Git command:
git clone git://git.savannah.gnu.org/libmatheval.git
For other ways to obtain GNU libmatheval, please see How to get GNU Software.
Documentation
The GNU libmatheval manual is available online in a number of formats.
Further information
The GNU libmatheval Savannah page has some additional information about GNU libmatheval.
GNU libmatheval bug reports and fixes, as well as improvement suggestions, should be directed to bug-libmatheval mailing list.
GNU project incorporates some other libraries related to mathematical calculations. Most notable of these is GNU Scientific Library.