calc.py

from multiprocessing.pool import Pool

a = 0.05 #float(raw_input("a: "))
b = 0.05 #float(raw_input("b: "))
d = 0.05 #float(raw_input("d: "))
#N = int(raw_input("numero di passi: "))
steps=100
sum = float(0.0)
oldSum = float(0.0)

def compute(N):
    # oldSum = sum
    oldSum = 0
    sum = float(0.0)
    factor = ((a*b*d/(N**2))**2)
    for i in range(N):
        #print sum
        for j in range(N):
            for n in range(N):
                for m in range(N):
                    sum += factor/(d**2 + (a*n/N-b*j/N)**2 + (a*m/N-b*i/N)**2)**2

    diff = (sum - oldSum)/sum
    print N,sum,diff


if __name__ == "__main__":
    p = Pool(processes=8)

    nums = [i for i in range(1,int(steps+1))]

    p.map(compute, nums)
    p.close()
    p.join()