python，将三角函数绘制成二维数组

Question

我是Python新手，在这种情况下，我想将我的函数放入二维数组中，这样我就可以绘制函数。这是我的三角形函数，我将其用于模糊逻辑:

def triangle (z,a,b,c):
    if (z<=a) | (z>=c):
        y = 0
    elif (a<=z) & (z<=b):
        y = (z-a) / (b-a)
    elif (b<=z) & (z<=c):
        y = (b-z) / (c-b)
    return y

我正在尝试使用 numpy 制作数组，np.linspace 但我无法完成它，我尝试过使用模糊库，但没有任何效果。

Answer 1

看起来a, b, c是常量，z是a之间的np.linspace，和c。

您可以使用Boolean Indexing , SciPy cookbook/Indexing

a = 1
b = 2
c = 3

def triangle (z, a = a, b = b, c = c):
    y = np.zeros(z.shape)
    y[z <= a] = 0
    y[z >= c] = 0
    first_half = np.logical_and(a < z, z <= b)
    y[first_half] = (z[first_half]-a) / (b-a)
    second_half = np.logical_and(b < z, z < c)
    y[second_half] = (c-z[second_half]) / (c-b)
    return y

z = np.linspace(a, c, num = 51)
y = triangle(z, a, b, c)

q = np.vstack((z, y)) # shape = (2, 50) ... [[z, z, z, ...], [y, y, y, ...]]
q =  q.T # shape = (50, 2) ... [[z, y], [z, y], ....]

<小时/>

当您在比较表达式中使用 numpy ndarray 时，结果是一个 bool 数组:

>>> q = np.linspace(0, 20, num = 50)
>>> print(q)
[  0.           0.40816327   0.81632653   1.2244898    1.63265306
   2.04081633   2.44897959   2.85714286   3.26530612   3.67346939
   4.08163265   4.48979592   4.89795918   5.30612245   5.71428571
   6.12244898   6.53061224   6.93877551   7.34693878   7.75510204
   8.16326531   8.57142857   8.97959184   9.3877551    9.79591837
  10.20408163  10.6122449   11.02040816  11.42857143  11.83673469
  12.24489796  12.65306122  13.06122449  13.46938776  13.87755102
  14.28571429  14.69387755  15.10204082  15.51020408  15.91836735
  16.32653061  16.73469388  17.14285714  17.55102041  17.95918367
  18.36734694  18.7755102   19.18367347  19.59183673  20.        ]
>>> print(q < 5)
[ True  True  True  True  True  True  True  True  True  True  True  True
  True False False False False False False False False False False False
 False False False False False False False False False False False False
 False False False False False False False False False False False False
 False False]
>>> print(q > 15)
[False False False False False False False False False False False False
 False False False False False False False False False False False False
 False False False False False False False False False False False False
 False  True  True  True  True  True  True  True  True  True  True  True
  True  True]
>>> print(np.logical_and(q > 5, q < 15))
[False False False False False False False False False False False False
 False  True  True  True  True  True  True  True  True  True  True  True
  True  True  True  True  True  True  True  True  True  True  True  True
  True False False False False False False False False False False False
 False False]
>>> 

您可以使用 bool 数组选择数组中满足您的条件的部分:

>>> q[np.logical_and(q > 7, q < 11)]
array([  7.34693878,   7.75510204,   8.16326531,   8.57142857,
         8.97959184,   9.3877551 ,   9.79591837,  10.20408163,  10.6122449 ])
>>> 

当您在赋值语句中使用 bool 索引时，右侧仅分配给比较为True的索引:

>>> q[np.logical_and(q > 7, q < 11)] = -1
>>> print(q)
[  0.           0.40816327   0.81632653   1.2244898    1.63265306
   2.04081633   2.44897959   2.85714286   3.26530612   3.67346939
   4.08163265   4.48979592   4.89795918   5.30612245   5.71428571
   6.12244898   6.53061224   6.93877551  -1.          -1.          -1.          -1.
  -1.          -1.          -1.          -1.          -1.          11.02040816
  11.42857143  11.83673469  12.24489796  12.65306122  13.06122449
  13.46938776  13.87755102  14.28571429  14.69387755  15.10204082
  15.51020408  15.91836735  16.32653061  16.73469388  17.14285714
  17.55102041  17.95918367  18.36734694  18.7755102   19.18367347
  19.59183673  20.        ]
>>>