如何格式化此文件，以避免出错？math.cos（）错误

Question

我试图用python解决这个精确的方程，但似乎不知道如何解决

import sympy
import scipy
import numpy


x = sympy.symbols("x")
y = sympy.symbols("y")
M= (1/x + 2*(y**2)*x)
N= (2*y*(x**2) - numpy.cos(y))
My = scipy.diff(M,y)
Nx = scipy.diff(N,x)
print('My=',My,'and Nx=',Nx,'so the equation is NOT an exact equation.')
# NOTE that M is simpler than N, so we use mu(y) for our integrating factor
Q=(Nx-My)/M
print('Q=',Q,'which is only a function of y')
# Using dsolve to find mu
mu=scipy.Function('mu')
IntFact=scipy.dsolve(scipy.diff(mu(y),y)-Q*mu(y),mu(y))
print(IntFact) # Any C will do (except 0 of course), so let C1 = 1
IntFact=scipy.exp(2*y)/y
newM=M*IntFact
newN=N*IntFact
My=scipy.diff(newM,y)
Nx=scipy.diff(newN,x)
print("New ODE is",newM,"+ (",newN.simplify(),")y' = 0")
print('My=',My,'and Nx=',Nx,'so the equation is now an exact equation.')
# Find F(x,y)
intMx=scipy.integrate(newM,x)
intNy=scipy.integrate(newN,y)
print('The integral of M dx is',intMx)
print('The integral of N dy is',intNy)
print('So F(x,y)=',intNy,'and the solution is',intNy,'= C')

主要错误在于这一行

N= (2*y*(x**2) - numpy.cos(y)) 

我不知道如何格式化它，所以我没有得到这个错误

TypeError: loop of ufunc does not support argument 0 of type Symbol which has no callable cos method

我已经尝试使用将cos（y）格式化为符号

cos = sympy.symbols("cos")

但我得到了一个错误，比如：

TypeError: 'Symbol' object is not callable

特别是因为这条线

  N= (2*y*(x**2) - cos(y))

Answer 1

您使用了错误的cos函数实现

NumPy的cos函数基本上以一个数字或一个数字数组作为参数（或可以被视为一个数字数组的东西）。此版本的cos函数不将符号作为输入

现在，Symphy有自己的三角函数，do接受符号。这是Symphy的cos函数的页面：https://docs.sympy.org/latest/modules/functions/elementary.html#cos