while循环嵌套在for循环中仅执行for循环的第一次迭代

Question

我遇到了嵌套在for循环中的while循环的问题。它在for循环的第一次迭代中完美执行，但for循环在所有其他迭代上跳过while循环。

我想用for循环的每个迭代的while循环执行次数nsteps填充列表nsteps_list。一个预期的答案将会像List = [17,16,16,14,15,13,​​12,15 ...]那样，但是发生的所有事情是List = [17,0,0,0,0,0 ...]

循环代码在这里：

# Bisection Method 

minn = np.arange(.00001, .001, 0.00005) 
nsteps_list = [0.0] * (len(minn)) # Rewrite each index with nsteps as iterating through 
nsteps = 0 

for i in range(0, len(minn) - 1): 

    while math.fabs(fx_2) > minn[i]: 

     if fx_2 > 0: 
      x_3 = x_2 
      print "UPDATE: x_3 = " + str(x_2) 

     elif fx_2 < 0: 
      x_1 = x_2 
      print "UPDATE: x_1 = " + str(x_2) 

     x_2 = 0.5 * (x_1 + x_3) 
     fx_2 = func(x_2) 
     nsteps += 1 

    print nsteps 
    nsteps_list[i] = nsteps 
    nsteps = 0 

print "List: " + str(nsteps_list) 

我从尝试，它通过对循环迭代精细知道，但它未能返回到while循环，所以n步来重置0从不改变，我的列表填充0。

以下是完整的代码，在上下文中：

#!/usr/bin/python 

import matplotlib.pylab as plt 
import numpy as np 
import math 


# Parabola = 3x^2-9x+2 ==> Has minimum and 2 real roots 

def func(n): # Defining function to get f(x) for each x for parabola 

    a = 3 
    b = -9 
    c = 2 

    fx = a * n * n + b * n + c 
    return fx 


# Calling parabola function on values in x 
x = np.arange(-2.0, 4.0, 0.2) 
y = func(x) 

plt.figure(1) 
plt.plot(x, y) 
plt.plot(x, x * 0) 

# Declare Variables for bisection method 

x_1 = 2.0 
x_3 = 3.0 
x_2 = 0.5 * (x_1 + x_3) 

fx_1 = func(x_1) 
fx_2 = func(x_2) 
fx_3 = func(x_3) 

if fx_1 >= 0: 
    print "Warning: Variable x_1 not initialised correctly." 
if fx_3 <= 0: 
    print "Warning: Variable x_3 not initialised correctly." 

# Bisection Method 

minn = np.arange(.00001, .001, 0.00005) 
nsteps_list = [0.0] * (len(minn)) # Rewrite each index with nsteps as iterating through 
nsteps = 0 

for i in range(0, len(minn) - 1): 

    while math.fabs(fx_2) > minn[i]: 

     if fx_2 > 0: 
      x_3 = x_2 
      print "UPDATE: x_3 = " + str(x_2) 

     elif fx_2 < 0: 
      x_1 = x_2 
      print "UPDATE: x_1 = " + str(x_2) 

     x_2 = 0.5 * (x_1 + x_3) 
     fx_2 = func(x_2) 
     nsteps += 1 

    print nsteps 
    nsteps_list[i] = nsteps 
    nsteps = 0 

print "List: " + str(nsteps_list) 

print "x_2 = " + str(x_2) + " and f(x_2) = " + str(fx_2) + "." 

plt.figure(2) 
plt.plot(np.log10(minn), nsteps_list) 
plt.figure(1) 
plt.plot(x_2, fx_2, "mo") 

plt.show() 

所以我需要这个阵列上对日志相应明尼苏达州值的图表绘制。有什么想法吗？

Answer 1

我调试了你的程序。 在第一个for循环交互之后，while循环运行17次。 i从0递增到1，并尝试再次评估while循环。

在这个pointvalue的fx_2这里是-8.63145396579057e-06 和minn[1]是6.0000000000000002e-05

所以fx_2的绝对值大于少min[i]其中i==1，因此不允许再次进入内环路，吐出零代替nsteps。

由于我不是一个数学知识，我建议你再看看你想要计算的东西。