After my initial encountering with OpenCL, I wanted to explore more. So I wrote a small program to calculate Pi .
This uses a very simple algorithm to calculate Pi
- Inscribe a circle in a square
- Randomly generate points in the square
- Determine the number of points in the square that are also in the circle
- Let r be the number of points in the circle divided by the number of points in the square
- PI ~ 4 r
- Note that the more points generated, the better the approximation
This gave the value of Pi as 3.141172 . Pretty decent, I suppose 
The code
import pyopencl as cl
import numpy
import random
class circle(object):
def __init__(self, r=100):
self.r = r
def inside_the_circle(self, x, y):
if x**2+y**2 <= r**2:
return 1
else:
return 0
class CL:
def __init__(self, size=1000):
self.size = size
self.ctx = cl.create_some_context()
self.queue = cl.CommandQueue(self.ctx)
def load_program(self):
f = """
__kernel void picalc(__global float* a, __global float* b, __global float* c)
{
unsigned int i = get_global_id(0);
if (a[i]*a[i]+ b[i]*b[i] < 100*100)
{
c[i] = 1;
}
else
{
c[i]=0;
}
}
"""
self.program = cl.Program(self.ctx, f).build()
def popcorn(self):
mf = cl.mem_flags
x = [random.uniform(-100,100) for i in range(self.size)]
y = [random.uniform(-100,100) for i in range(self.size)]
self.a = numpy.array(x, dtype=numpy.float32)
self.b = numpy.array(y, dtype=numpy.float32)
self.a_buf = cl.Buffer(self.ctx, mf.READ_ONLY | mf.COPY_HOST_PTR, hostbuf=self.a)
self.b_buf = cl.Buffer(self.ctx, mf.READ_ONLY | mf.COPY_HOST_PTR, hostbuf=self.b)
self.dest_buf = cl.Buffer(self.ctx, mf.WRITE_ONLY, self.b.nbytes)
def execute(self):
self.program.picalc(self.queue, self.a.shape, None, self.a_buf,
self.b_buf, self.dest_buf)
self.c = numpy.empty_like(self.a)
cl.enqueue_read_buffer(self.queue, self.dest_buf, self.c).wait()
def calculate_pi(self):
number_in_circle = 0
for i in self.c:
number_in_circle = number_in_circle + i
pi = number_in_circle*4 / self.size
print 'pi = ', pi
if __name__ == '__main__':
ex = CL(1000000)
ex.load_program()
ex.popcorn()
ex.execute()
ex.calculate_pi()
