问题描述
让我们说我们有三个复矩阵和一个具有这些矩阵的耦合微分方程组.
Lets say we have three complex matrices and a system of coupled differential equations with these matrices.
import numpy, scipy
from numpy import (real,imag,matrix,linspace,array)
from scipy.integrate import odeint
import matplotlib.pyplot as plt
def system(x,t):
a1= x[0];a3= x[1];a5= x[2];a7= x[3];
a2= x[4];a4= x[5];a6= x[6];a8= x[7];
b1= x[8];b3= x[9];b5= x[10];b7= x[11];
b2= x[12];b4= x[13];b6= x[14];b8= x[15];
c1= x[16];c3= x[17];c5= x[18];c7= x[19];
c2= x[20];c4= x[21];c6= x[22];c8= x[23];
A= matrix([ [a1+1j*a2,a3+1j*a4],[a5+1j*a6,a7+1j*a8] ])
B= matrix([ [b1+1j*b2,b3+1j*b4],[b5+1j*b6,b7+1j*b8] ])
C= matrix([ [c1+1j*c2,c3+1j*c4],[c5+1j*c6,c7+1j*c8] ])
dA_dt= A*C+B*C
dB_dt= B*C
dC_dt= C
list_A_real= [dA_dt[0,0].real,dA_dt[0,1].real,dA_dt[1,0].real,dA_dt[1,1].real]
list_A_imaginary= [dA_dt[0,0].imag,dA_dt[0,1].imag,dA_dt[1,0].imag,dA_dt[1,1].imag]
list_B_real= [dB_dt[0,0].real,dB_dt[0,1].real,dB_dt[1,0].real,dB_dt[1,1].real]
list_B_imaginary= [dB_dt[0,0].imag,dB_dt[0,1].imag,dB_dt[1,0].imag,dB_dt[1,1].imag]
list_C_real= [dC_dt[0,0].real,dC_dt[0,1].real,dC_dt[1,0].real,dC_dt[1,1].real]
list_C_imaginary= [dC_dt[0,0].imag,dC_dt[0,1].imag,dC_dt[1,0].imag,dC_dt[1,1].imag]
return list_A_real+list_A_imaginary+list_B_real+list_B_imaginary+list_C_real+list_C_imaginary
t= linspace(0,1.5,1000)
A_initial= [1,2,2.3,4.3,2.1,5.2,2.13,3.43]
B_initial= [7,2.7,1.23,3.3,3.1,5.12,1.13,3]
C_initial= [0.5,0.9,0.63,0.43,0.21,0.5,0.11,0.3]
x_initial= array( A_initial+B_initial+C_initial )
x= odeint(system,x_initial,t)
plt.plot(t,x[:,0])
plt.show()
我基本上有两个问题:
-
如何减少代码?通过减少,我的意思是,有一种方法可以通过不单独写下所有组件,而是在解决系统问题的同时处理矩阵来实现. ODE?
How to reduce my code? By reduce I meant, is there a way to do this by not writing down all the components separately ,but handling with the matrices while solving the system of ODE?
不是相对于 t (代码的最后两行)绘制矩阵元素,而是如何绘制特征值(绝对值)(例如,矩阵A的特征值的绝对值是否是t)的函数?
Instead of plotting elements of the matrices with respect to t (the last 2 lines of my code), how can I plot Eigenvalues (absolute values) (lets say, the abs of eigenvalues of matrix A as a function of t)?
推荐答案
今年早些时候,我为scipy.integrate.odeint
创建了一个包装器,从而可以轻松地求解复杂的数组微分方程:"> https://github.com/WarrenWeckesser/odeintw
Earlier this year I created a wrapper for scipy.integrate.odeint
that makes it easy to solve complex array differential equations: https://github.com/WarrenWeckesser/odeintw
您可以使用git检出整个软件包,并使用脚本setup.py
安装它,或者可以获取一个基本文件 _odeintw.py
,将其重命名为odeintw.py
,然后将其复制到您需要的任何位置.以下脚本使用功能odeintw.odeintw
来解决您的系统.它通过将三个矩阵A
,B
和C
堆叠到形状为(3,2,2)的三维数组M
中来使用odeintw
.
You can check out the whole package using git and install it using the script setup.py
, or you can grab the one essential file, _odeintw.py
, rename it to odeintw.py
, and copy it to wherever you need it. The following script uses the function odeintw.odeintw
to solve your system. It uses odeintw
by stacking your three matrices A
, B
and C
into a three-dimensional array M
with shape (3, 2, 2).
您可以使用numpy.linalg.eigvals
计算A(t)
的特征值.该脚本显示了一个示例和一个图.特征值很复杂,因此您可能必须进行一些实验才能找到一种可视化它们的好方法.
You can use numpy.linalg.eigvals
to compute the eigenvalues of A(t)
. The script shows an example and a plot. The eigenvalues are complex, so you might have to experiment a bit to find a nice way to visualize them.
import numpy as np
from numpy import linspace, array
from odeintw import odeintw
import matplotlib.pyplot as plt
def system(M, t):
A, B, C = M
dA_dt = A.dot(C) + B.dot(C)
dB_dt = B.dot(C)
dC_dt = C
return array([dA_dt, dB_dt, dC_dt])
t = np.linspace(0, 1.5, 1000)
#A_initial= [1, 2, 2.3, 4.3, 2.1, 5.2, 2.13, 3.43]
A_initial = np.array([[1 + 2.1j, 2 + 5.2j], [2.3 + 2.13j, 4.3 + 3.43j]])
# B_initial= [7, 2.7, 1.23, 3.3, 3.1, 5.12, 1.13, 3]
B_initial = np.array([[7 + 3.1j, 2.7 + 5.12j], [1.23 + 1.13j, 3.3 + 3j]])
# C_initial= [0.5, 0.9, 0.63, 0.43, 0.21, 0.5, 0.11, 0.3]
C_initial = np.array([[0.5 + 0.21j, 0.9 + 0.5j], [0.63 + 0.11j, 0.43 + 0.3j]])
M_initial = np.array([A_initial, B_initial, C_initial])
sol = odeintw(system, M_initial, t)
A = sol[:, 0, :, :]
B = sol[:, 1, :, :]
C = sol[:, 2, :, :]
plt.figure(1)
plt.plot(t, A[:, 0, 0].real, label='A(t)[0,0].real')
plt.plot(t, A[:, 0, 0].imag, label='A(t)[0,0].imag')
plt.legend(loc='best')
plt.grid(True)
plt.xlabel('t')
A_evals = np.linalg.eigvals(A)
plt.figure(2)
plt.plot(t, A_evals[:,0].real, 'b.', markersize=3, mec='b')
plt.plot(t, A_evals[:,0].imag, 'r.', markersize=3, mec='r')
plt.plot(t, A_evals[:,1].real, 'b.', markersize=3, mec='b')
plt.plot(t, A_evals[:,1].imag, 'r.', markersize=3, mec='r')
plt.ylim(-200, 1200)
plt.grid(True)
plt.title('Real and imaginary parts of the eigenvalues of A(t)')
plt.xlabel('t')
plt.show()
以下是脚本生成的图:
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