Write less code in C typedef struct linearode_{
int num_d, num_s;
double dt;
double **a;
double **x;
} LinearODE;
int LinearODE_run(LinearODE *self)
{
int s, d1, d2;
for (s = 1; s < self->num_s; ++s){
for (d1 = 0; d1 < self->num_d; ++d1){
self->x[s][d1] = self->x[s-1][d1];
for (d2 = 0; d2 < self->num_d; ++d2){
self->x[s][d1] += self->dt * \
self->a[d1][d2] * self->x[s-1][d2];
}
}
}
return 0;
}
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... and in Python! from railgun import SimObject, relpath
class LinearODE(SimObject):
_clibname_ = 'liblode.so'
_clibdir_ = relpath('.', __file__)
_cmembers_ = [
'num_d',
'num_s = 10000',
'double dt = 0.001',
'double a[d][d]',
'double x[s][d]',
]
_cfuncs_ = ["x run()"]
lode = LinearODE(num_d=2)
lode.a = [[0, 1], [-1, 0]]
lode.x[0] = [1, 0]
x = lode.run()
import pylab
pylab.plot(x)
pylab.show()
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The pair of c and python code above is a very short and complete example!
If you want to write fast program for numerical simulations, you will always end up with writing it in C (or C++ or FORTRAN, these low-level languages). Although we have great python packages (not only) for numerical simulation such as Numpy/Scipy, Pyrex, Cython, Psyco and so on, sometimes these are not enough. On the other hand, writing code in C is stressful, especially things like allocating memory and read/write data which do not require speed so much. So, next thing you want is to call C function from python and let python do all these stuff (which python is good at!). Using ctypes, this is very easy.
But you may want much easier way! RailGun automatically generates a python class which loads functions from C shared library, allocate consistent arrays, provide argument checks at python side before the argument is passed to C function, and let you easily access C variables via python. All you need to do is to follow certain coding style when you write C program so that RailGun can load functions automatically.
Installation:
easy_install railgun # using setuptools
pip install railgun # using pip
Contents:
RailGun’s repository is http://bitbucket.org/tkf/railgun/. See samples in source code or here.