无法绘制我的函数：返回array（a，dtype，copy = False，order = order）TypeError：float（）参数必须为字符串或数字

我正在尝试绘制一个函数，该函数给出几个散点图的角度的反正切（这是一个物理实验）：

这是我的代码：

import numpy as np
import matplotlib.pyplot as plt

filename='rawPhaseDataf2f_17h_15m.dat'
datatype=np.dtype( [('Shotnumber',np.dtype('>f8')),('A1',np.dtype('>f8')),      ('A2',np.dtype('>f8')), ('f2f',np.dtype('>f8')), ('intensity',np.dtype('>f8'))])
data=np.fromfile(filename,dtype=datatype)

#time=data['Shotnumber']/9900 # reprate is 9900 Hz -> time in seconds
A1=data['A1']
A2=data['A2']

#np.sort()
i=range(1,209773) 

def x(i) :
    return arctan((A1.item(i)/A2.item(i))*(i/209772))
def y(i) : 
    return i*2*pi/209772

plot(x,y)

plt.figure('Scatterplot')
plt.plot(A1,A2,',') #Scatterplot
plt.xlabel('A1')
plt.ylabel('A2')

plt.figure('2D Histogram')
plt.hist2d(A1,A2,100) # 2D Histogram
plt.xlabel('A1')
plt.ylabel('A2')

plt.show()

我的错误是：

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell   /sitecustomize.py", line 540, in runfile
    execfile(filename, namespace)
  File "/home/nelly/Bureau/ Téléchargements/Kr4  Experiment/read_rawPhaseData.py", line 21, in <module>
    plot(x,y)
  File "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 2987, in plot
ret = ax.plot(*args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 4138, in plot
self.add_line(line)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 1497, in add_line
self._update_line_limits(line)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 1508, in _update_line_limits
path = line.get_path()
  File "/usr/lib/pymodules/python2.7/matplotlib/lines.py", line 743, in get_path
    self.recache()
  File "/usr/lib/pymodules/python2.7/matplotlib/lines.py", line 420, in recache
    x = np.asarray(xconv, np.float_)
  File "/usr/lib/python2.7/dist-packages/numpy/core/numeric.py", line 460, in asarray
    return array(a, dtype, copy=False, order=order)
TypeError: float() argument must be a string or a number

我知道问题出在哪里plot(x,y)。我认为我的错误来自定义x和y。A1和A2是矩阵，N是点的数量，是矩阵Ak的索引。我想拥有arctan(A1k/A2k)*(k/N)。