使用if语句的网格和用户定义函数的含糊真值 [英] Ambiguous truth value for meshgrid and user-defined functions using if-statement

问题描述

让我们假设我的函数 f(x，y)足够平滑.但是，某些值仅在极限的意义上存在.以例如sin(x)/x x=0 的值只存在于极限 x -> 0 内.在一般情况下，我用 if 语句处理此问题.

Let's assume that I have a function f(x,y) being sufficiently smooth. Yet some values only exist in the sense of a limit. Take e.g. sin(x)/ x the value for x=0 only exists in the limit x -> 0. In the general case I handle this with an if statement.

如果我在带有 meshgrid 的情节中使用它，则会收到错误消息:

If I use this in a plot with meshgrid I get an error message:

ValueError:包含多个元素的数组的真值不明确.使用 a.any() 或 a.all()

我真的必须运行两个 for 循环来填充 z-array 还是有办法使用 meshgrid?

Do I really have to run two for loops to fill an z-array or is there a way to use meshgrid?

最小工作示例:

import matplotlib.pyplot as plt
import numpy as np

def test(x,y):
    a=1.0/(1+x*x)
    if y==0:
        b=1
    else:
        b=np.sin(y)/y
    return(a * b)

if __name__=='__main__':
    X = linspace(-5, 5, 100)
    Y = linspace(-5, 5, 100)
    X,Y = meshgrid(X, Y)
    Z =test(X,Y)

    fig = plt.figure(figsize=(8,6))
    ax = fig.add_subplot(1,1,1, projection='3d')
    ax.plot_surface(X, Y, Z, rstride=8, cstride=8, alpha=0.25)
    plt.show()

推荐答案

要仅将值分配给 Numpy 数组的某些元素，您可以简单地使用索引，

To assign values only to some elements of a Numpy array you can simply use indexing,

import numpy as np

def test(x, y):
    a = 1.0/(1+x*x)
    b = np.ones(y.shape)
    mask = (y!=0)
    b[mask] = np.sin(y[mask])/y[mask]
    return a*b

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