from math import *
from random import *
from visual.graph import *

N=100000
MEASURE=1

pic=gdisplay(x=600,y=0,width=400,height=200,xmin=-2.0,xmax=2.0,ymin=0.0,
             foreground=color.black, background=color.white)
p=ghistogram(gdisplay=pic,bins=arange(-2.0,2.0,0.1), accumulate=1,color=color.blue)

dist=[]

delta=0.5
b=1000.0
alpha=1.0

mean=0.0
meansq=0.0
## loop over measurements

    
    mc=0
    x=random()
    for i in range(0,N):
        xtrial=x+delta*(random()-0.5)
        if ((xtrial>b) or (xtrial<-b)):
             continue
        w=exp(-alpha*(xtrial*xtrial-x*x))
            
        if (random()<=w):
            x=xtrial
                
        mc+=x*x
        dist.append(x)
                            
    mc/=N
    p.plot(dist)
# accumulate the mean and its square
    

mean/=MEASURE
meansq/=MEASURE

## print out mean and its error