Description:

GNU libmatheval is a library which contains several procedures that
make it possible to create an in-memory tree from the string
representation of a mathematical function over single or multiple
variables. This tree can be used later to evaluate a function for
specified variable values, to create a corresponding tree for the
function derivative over a specified variable, or to write a textual
tree representation to a specified string. The library exposes C and
Fortran 77 interfaces.