'''二分法'''
import numpy
as np
d =
20
s =
36.234
a=
0.01; b=
3.14;
global step
step=
0
def f(x,d,s):
return x-np.sin(x)-
8*s/(d*d)*np.sin(x/
2)*np.sin(x/
2)
def erfen(a,b,d,s):
global step
fhalf=f((a+b)/
2,d,s);
half=(a+b)/
2;
fa=f(a,d,s);fb=f(b,d,s);
step=step+
1;
if (fa==
0 ):
return a
if (fb==
0):
return a
if(fhalf==
0):
return fhalf
if np.sqrt(abs(fa*fb))<
1e-10:
return a
if fhalf*fb<
0:
return erfen(half,b,d,s)
else:
return erfen(a,half,d,s)
x=erfen(a,b,d,s)
r=np.sqrt(d*d/(
1-np.cos(x))/
2.0)
print(r,x)