14.26.15 problem 15

Internal problem ID [2788]
Book : Differential equations and their applications, 4th ed., M. Braun
Section : Chapter 3. Systems of differential equations. Section 3.13 (Solving systems by Laplace transform). Page 370
Problem number : 15
Date solved : Tuesday, March 04, 2025 at 02:42:39 PM
CAS classification : system_of_ODEs

\begin{align*} \frac {d}{d t}x_{1} \left (t \right )&=3 x_{1} \left (t \right )\\ \frac {d}{d t}x_{2} \left (t \right )&=x_{1} \left (t \right )+3 x_{2} \left (t \right )\\ \frac {d}{d t}x_{3} \left (t \right )&=3 x_{3} \left (t \right )\\ \frac {d}{d t}x_{4} \left (t \right )&=2 x_{3} \left (t \right )+3 x_{4} \left (t \right ) \end{align*}

With initial conditions

\begin{align*} x_{1} \left (0\right ) = 1\\ x_{2} \left (0\right ) = 1\\ x_{3} \left (0\right ) = 1\\ x_{4} \left (0\right ) = 1 \end{align*}

✓ Maple. Time used: 0.037 (sec). Leaf size: 39

ode:=[diff(x__1(t),t) = 3*x__1(t), diff(x__2(t),t) = x__1(t)+3*x__2(t), diff(x__3(t),t) = 3*x__3(t), diff(x__4(t),t) = 2*x__3(t)+3*x__4(t)]; 
ic:=x__1(0) = 1x__2(0) = 1x__3(0) = 1x__4(0) = 1; 
dsolve([ode,ic]);
 

\begin{align*} x_{1} \left (t \right ) &= {\mathrm e}^{3 t} \\ x_{2} \left (t \right ) &= \left (t +1\right ) {\mathrm e}^{3 t} \\ x_{3} \left (t \right ) &= {\mathrm e}^{3 t} \\ x_{4} \left (t \right ) &= \left (1+2 t \right ) {\mathrm e}^{3 t} \\ \end{align*}

✓ Mathematica. Time used: 0.006 (sec). Leaf size: 44

ode={D[x1[t],t]==3*x1[t],D[x2[t],t]==1*x1[t]+3*x2[t],D[x3[t],t]==3*x3[t],D[x4[t],t]==2*x3[t]+3*x4[t]}; 
ic={x1[0]==1,x2[0]==1,x3[0]==1,x4[0]==1}; 
DSolve[{ode,ic},{x1[t],x2[t],x3[t],x4[t]},t,IncludeSingularSolutions->True]
 

\begin{align*} \text {x1}(t)\to e^{3 t} \\ \text {x2}(t)\to e^{3 t} (t+1) \\ \text {x3}(t)\to e^{3 t} \\ \text {x4}(t)\to e^{3 t} (2 t+1) \\ \end{align*}

✓ Sympy. Time used: 0.157 (sec). Leaf size: 54

from sympy import * 
t = symbols("t") 
x__1 = Function("x__1") 
x__2 = Function("x__2") 
x__3 = Function("x__3") 
x__4 = Function("x__4") 
ode=[Eq(-3*x__1(t) + Derivative(x__1(t), t),0),Eq(-x__1(t) - 3*x__2(t) + Derivative(x__2(t), t),0),Eq(-3*x__3(t) + Derivative(x__3(t), t),0),Eq(-2*x__3(t) - 3*x__4(t) + Derivative(x__4(t), t),0)] 
ics = {} 
dsolve(ode,func=[x__1(t),x__2(t),x__3(t),x__4(t)],ics=ics)
 

\[ \left [ x^{1}{\left (t \right )} = C_{1} e^{3 t}, \ x^{2}{\left (t \right )} = C_{1} t e^{3 t} + C_{2} e^{3 t}, \ x^{3}{\left (t \right )} = C_{3} e^{3 t}, \ x^{4}{\left (t \right )} = 2 C_{3} t e^{3 t} + 2 C_{4} e^{3 t}\right ] \]