59 lines
967 B
Python
59 lines
967 B
Python
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def bisec(f, a, b, eps, nmax):
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"""
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Takes f:[a,b] -> |R and tries to compute the null point
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using bisection.
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"""
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if(f(a)*f(b) >= 0):
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raise ValueError("f(a)*f(b) >= 0")
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x_minus = a
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x_plus = b
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if(a > b):
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x_minus = b
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x_plus = a
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for i in range(nmax):
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x_minus, x_plus, err = bisec_one(x_minus, x_plus, f, eps)
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if(err < eps):
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break
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if(err < eps):
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return x_minus, err
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raise ValueError("bisection hit nmax")
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def bisec_one(x_minus, x_plus, f, eps):
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a = x_minus
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b = x_plus
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x_m = (b + a) / 2
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y_m = f(x_m)
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if(y_m < 0):
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if(y_m > -1*eps):
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return x_m, x_m, -y_m
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if(f(x_m)*f(b) >= 0):
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return a, x_m, -y_m
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return x_m, b, -y_m
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if(y_m < eps):
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return x_m, x_m, y_m
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if(f(a)*f(x_m) >= 0):
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return x_m, b, y_m
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return a, x_m, y_m
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if( __name__ == "__main__"):
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f1 = lambda x: x
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f2 = lambda x: x**3
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f3 = lambda x: -x + 1
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f4 = lambda x: -x**3 + 1
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fs = [f1, f2, f3, f4]
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for f in fs:
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print(bisec(f, -12, 10, 0.001, 100))
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