我正在尝试绘制sin(x)/x函数及其泰勒逼近图形。我使用的是Python 3和Pyzo。第一个图形绘制成功了,但是我遇到了一个问题,无法将来自Sympy模块的系列转换为可以工作的numpy表达式。
import numpy as np
import matplotlib.pyplot as plt
import sympy as sp
from sympy.abc import x
x = np.linspace(-10, 10, 100)
y = np.sin(x)/x #first function
plt.plot(x, y, 'k') #this is working fine
### this is a code that removes the "0(x**something)" part of
the series at the end
我在这里找到了它:http://pastebin.com/ZNQakWP7
def series(expr, x, x0, n, removeO=False):
"""
sympy bugs avoided
"""
# expr_series = expr.series(x, x0, n)
# return expr_series.removeO() if removeO else expr_series
expansion = list()
for t in expr.lseries(x, x0):
p = t.as_coeff_exponent(x)[1]
if p < n:
expansion.append(t)
else:
break
if not removeO:
expansion.append(sp.O(x**n))
return sp.Add(*expansion)
### my code continued ####
y_t=series(sp.sin(x)/x,x,0,6,removeO=True)
如果我现在查看y_t,我会得到这个近似值
out: x**4/120 - x**2/6 + 1
现在我尝试将其转换为numpy,以便像第一个函数一样绘制它。
f_t = lambdify(x, y_t,modules=['numpy'])
x = np.linspace(-10, 10, 100) #i do this because x has
#been a symbolic variable before
plt.plot(x, y_t, 'b') #this is where the problem occurs
我收到了第一个图形和第二个错误信息。
File "<console>", line 1, in <module>
File "F:\pyzo2013_0_2_2\lib\site-packages\matplotlib\pyplot.py", line 2832, in plot
ret = ax.plot(*args, **kwargs)
File "F:\pyzo2013_0_2_2\lib\site-packages\matplotlib\axes.py", line 3998, in plot
for line in self._get_lines(*args, **kwargs):
我该如何实现我的想法,绘制出从sympy产生的图形? 我另外一个想法是将sympy输出从系列转换为字符串,然后以某种方式解析为numpy表达式。在这里,我将非常感激任何帮助!