# Loops get slower as they run

Hello, I am trying to run a simulation in sage as part of my homework. The simulation itself is pretty fast and working fine. The problem starts when i try to run the simulation several times in a loop, then sage becomes incredibly slow in each repeat.

The program I wrote:

```
def poisson(lmu):
var('mu n')
g(mu,n)=(e^-mu * mu^n)/factorial(n)
num=random()
sum=g(lmu,0)
for i in xrange(1000):
if num<sum:
return i-1
else:
sum=sum+g(lmu,i)
def galtonwatson(mu,s,gens):
deaths=0
for i in range (gens):
N=1
n=0
while n<s and N!=0:
N=poisson(N*mu)
n=n+1
if N==0:
deaths=deaths+1
return (deaths/gens).N()
```

both of the functions works fine, then telling sage to fill a list of 10 arrays with the values, and checking how much time it took for each repeat:

```
L=np.array([[0,0]for i in range(9)])
for i in xrange (9):
t=time.time()
print i
L[i]= (i,galtonwatson(2,i,100))
print (time.time()-t)
```

Sage output is:

```
0
0.000202894210815
1
0.393799066544
2
0.893945932388
3
1.54169392586
4
2.87310600281
5
4.84653711319
6
9.23449707031
7
18.3007540703
8
35.5397469997
```

It ain't the first time that sage loops becomes slower and slower on the run, and I could'nt understand the reason when searching the net.

Thanks in advanced, David