python matplotlib quiver——画箭头、风场
作者:互联网
理解参考:https://blog.csdn.net/liuchengzimozigreat/article/details/84566650
以下实例
import numpy as np import matplotlib.pyplot as plt def function(x): return np.sum(x**2)#return x[0]**2 + x[1]**2 def _numerical_gradient_no_batch(f,x): h = 1e-4 grad = np.zeros_like(x) for idx in range(x.size): tmp_va1 = x[idx] x[idx] = float(tmp_va1) + h fxh1 =f(x) x[idx] = tmp_va1 -h fxh2 = f(x) grad[idx] = (fxh1- fxh2)/(2*h) x[idx] = tmp_va1 print("grad:"+str(grad)) return grad def numerical_gradient(f,X): if X.ndim == 1: return _numerical_gradient_no_batch(f,X) else: grad = np.zeros_like(X) for idx,x in enumerate(X): grad[idx] = _numerical_gradient_no_batch(f,x) return grad def function_2(x): if x.ndim == 1: return np.sum(x **2) else: return np.sum(x**2,axis=1) def tangent_line(f,x): d = numerical_gradient(f,x) print(d) y = f(x) - d * x return lambda t : d * t + y print(_numerical_gradient_no_batch(function_2,np.array([3.0,4.0]))) print(numerical_gradient(function_2,np.array([3.0,4.0]))) print(numerical_gradient(function_2,np.array([[3.0,4.0],[0.0,2.0],[3.0,0.0]]))) if __name__ =='__main__': x0= np.arange(-2,2.5,0.25) x1=np.arange(-2,2.5,0.25) X,Y= np.meshgrid(x0,x1) X = X.flatten() Y = Y.flatten() grad = numerical_gradient(function_2,np.array([X,Y])) plt.figure() plt.quiver(X,Y,-grad[0],-grad[1],angles="xy",color="#666666") plt.xlim([-2,2]) plt.ylim([-2,2]) plt.xlabel('x0') plt.ylabel('x1') plt.grid() plt.legend() plt.draw() plt.show()
标签:plt,quiver,idx,python,numerical,gradient,风场,np,grad 来源: https://www.cnblogs.com/xianhan/p/10401442.html