sympy collect返回dict，无法使用key访问

Question

我正在使用Collect函数来分离一些术语。 它返回一个Dict，我无法使用给定的键访问它。举个例子：

import sympy as sp
t = sp.Symbol('t')
K1,K2,K3,K4 = sp.symbols("K1 K2 K3 K4")
W,R,L,C = sp.symbols("omega R L C")
Vi_t = 10*sp.cos(W*t)
Vi_yp_t = (1/L)*sp.diff(Vi_t,t)
Yp = K3*sp.cos(W*t)+K4*sp.sin(W*t)
dYp = sp.diff(Yp,t)
d2Yp = sp.diff(dYp,t)
malha = d2Yp +(R/L)*dYp + (1/L*C)*Yp
malha_separada = sp.collect(malha,(sp.sin(W*t),sp.cos(W*t)),evaluate=False)

打印此项可提供：

我可以用malha_separada[1]访问密钥“1”，但是我用sin（omega*t）进行的任何尝试都会导致密钥错误。 符号，W，/ω。。。 有什么想法吗？你知道吗

Answer 1

必须使用sp.cos(W*t)和sp.sin(W*t)

import sympy as sp
t = sp.Symbol('t')
K1,K2,K3,K4 = sp.symbols("K1 K2 K3 K4")
W,R,L,C = sp.symbols("omega R L C")
Vi_t = 10*sp.cos(W*t)
Vi_yp_t = (1/L)*sp.diff(Vi_t,t)
Yp = K3*sp.cos(W*t)+K4*sp.sin(W*t)
dYp = sp.diff(Yp,t)
d2Yp = sp.diff(dYp,t)
malha = d2Yp +(R/L)*dYp + (1/L*C)*Yp
malha_separada = sp.collect(malha, (sp.sin(W*t), sp.cos(W*t)), evaluate=False)
print(malha_separada[1])
print(malha_separada[sp.cos(W*t)])
print(malha_separada[sp.sin(W*t)])

输出：

C*(K3*cos(omega*t) + K4*sin(omega*t))/L + R*(-K3*omega*sin(omega*t) + K4*omega*cos(omega*t))/L
-K3*omega**2
-K4*omega**2