I would strongly argue in favour of Fortran, in particular for Fortran 90 upwards. Some use Fortran in combination of C, and Fortran 2015 is expected to provide more support for this type of use. See also:
http://en.wikipedia.org/wiki/Fortran
Note added: I should also mention that the answer to the question of what constitutes the "best programming language", also depends on the type of applications one has in mind. The later editions of Mathematica (in particular Mathematica 8 and 9) are very good and powerful, capable of even performing parallel computations. Certainly, for the development stage, Mathematica (which has its own programming language - a very intuitive one) may be viewed as an almost indispensable computational tool.
You can try with MATLAB. One can code and create simulations. You have MATLAB equivalent OCTAVE on linux. It works on commandline. If you want to work on GUI install qtoctave. OCATVE is opensource and canbe used free of cost.