75.14.37 problem 363

Internal problem ID [16880]
Book : A book of problems in ordinary differential equations. M.L. KRASNOV, A.L. KISELYOV, G.I. MARKARENKO. MIR, MOSCOW. 1983
Section : Chapter 2 (Higher order ODEs). Section 14. Differential equations admitting of depression of their order. Exercises page 107
Problem number : 363
Date solved : Monday, March 31, 2025 at 03:34:35 PM
CAS classification : [[_3rd_order, _missing_x], [_3rd_order, _exact, _nonlinear], [_3rd_order, _with_linear_symmetries], [_3rd_order, _reducible, _mu_y2]]

\begin{align*} y^{\prime \prime \prime }&=3 y y^{\prime } \end{align*}

With initial conditions

\begin{align*} y \left (0\right )&=1\\ y^{\prime }\left (0\right )&=1\\ y^{\prime \prime }\left (0\right )&={\frac {3}{2}} \end{align*}

✓ Maple. Time used: 0.075 (sec). Leaf size: 11

ode:=diff(diff(diff(y(x),x),x),x) = 3*y(x)*diff(y(x),x); 
ic:=y(0) = 1, D(y)(0) = 1, (D@@2)(y)(0) = 3/2; 
dsolve([ode,ic],y(x), singsol=all);
 

\[ y = \frac {4}{\left (x -2\right )^{2}} \]

✗ Mathematica

ode=D[y[x],{x,3}]==3*y[x]*D[y[x],x]; 
ic={y[0]==1,Derivative[1][y][0] ==1,Derivative[2][y][0] ==3/2}; 
DSolve[{ode,ic},y[x],x,IncludeSingularSolutions->True]
 

{}

✗ Sympy

from sympy import * 
x = symbols("x") 
y = Function("y") 
ode = Eq(-3*y(x)*Derivative(y(x), x) + Derivative(y(x), (x, 3)),0) 
ics = {y(0): 1, Subs(Derivative(y(x), x), x, 0): 1, Subs(Derivative(y(x), (x, 2)), x, 0): 3/2} 
dsolve(ode,func=y(x),ics=ics)
 

NotImplementedError : The given ODE Derivative(y(x), x) - Derivative(y(x), (x, 3))/(3*y(x)) cannot be solved by the factorable group method