For easier low-level math-ish programming, I chose to learn Fortran. Actually, it is the free, GFortran implementation of Fortran 90. And it ran very fast! It could calculate the Euler-Mascheroni constant in up to 2,147,483,647 iterations quickly.
Using a simple method, I tried to numerically solve a non-linear second-order ODE... Well, actually it is a pendulum motion with a large amplitude. It solves and produces the time versus angle data in a blink with a fair precision (dt = .01 s)...
Red: data obtained from Fortran program, Green: sinusoidal approximation of the motion, Blue: plot for simple pendulum with small oscillation with same parameters.
Out of the box, GNU Emacs integrates nicely with GFortran, with code highlighting and debugging (I haven't tried the debugging yet).