ส่งงาน week12

week12/Initial-Value.py

+#Bracketing minimum
+def f(x) : return x**2-2*x+1
+from matplotlib import pyplot as plt
+import numpy as np
+x=[x/10 for x in range(-20,20,1)]
+y=[f(xi) for xi in x]
+print(x)
+print(y)
+a,b=-2,2
+fa,fb=f(a),f(b)
+plt.plot(x,y,"g-")
+plt.show()
+
+#next
+def bracket(f, **kwargs):
+    a = float(kwargs['a'])
+    b = float(kwargs['b'])
+    h = float(kwargs['h'])
+    xi = a
+    oldf = f(xi)
+    xi += h
+    newf = f(xi)
+    while newf < oldf :
+        oldf = newf
+        xi += h
+        newf = f(xi)
+    xi -= h
+    print('Solution xi',xi,f(xi))
+bracket(f,a=-2,b=2,h=0.01)
+
+#Golden Section Search
+import math
+R = (-1 + 5**0.5)/2
+def n(a=-2,b=2,ebs=10**-9) :
+    from math import log as ln
+    return int(-ln(R)*ln(eps/abs(b-a)))
+def search(f,a,b,tol=1.0e-9):
+    nIter = n(a,b)
+    0.618033989
+    C = 1.0 - R
+    # First telescoping
+    x1 = R*a + C*b; x2 = C*a + R*b
+    f1 = f(x1); f2 = f(x2)
+    # Main loop
+    for i in range(nIter):
+        if f1 > f2:
+            a = x1
+            x1 = x2; f1 = f2
+            x2 = C*a + R*b; f2 = f(x2)
+        else:
+            b = x2
+            x2 = x1; f2 = f1
+            x1 = R*a + C*b; f1 = f(x1)
+
+    if f1 < f2: return x1,f1
+    return x2,f2
+search(f,-2,2)