Internal
problem
ID
[8743]
Book
:
Own
collection
of
miscellaneous
problems
Section
:
section
1.0
Problem
number
:
32
Date
solved
:
Sunday, March 30, 2025 at 01:29:23 PM
CAS
classification
:
[[_homogeneous, `class C`], _rational, [_Abel, `2nd type`, `class A`]]
Time used: 0.336 (sec)
Solve
Let
Solving for possible values of
Using these values now it is possible to easily solve for
In canonical form, the ODE is
An ode of the form
In this case, it can be seen that both
Applying the
transformation
Or
Or
Which is now solved as separable in
The ode
is separable as it can be written as
Where
Integrating gives
Taking the exponential of both sides the solution becomes
We now need to find the singular solutions, these are found by finding for what values
for
Now we go over each such singular solution and check if it verifies the ode itself and any initial conditions given. If it does not then the singular solution will not be used.
Therefore the solutions found are
Converting
Converting
Converting
Using the solution for
And replacing back terms in the above solution using
Or
Then the solution in
Using the solution for
And replacing back terms in the above solution using
Or
Then the solution in
Using the solution for
And replacing back terms in the above solution using
Or
Then the solution in
Solving for
Summary of solutions found
Time used: 0.633 (sec)
Solve
Writing the ode as
The condition of Lie symmetry is the linearized PDE given by
To determine
Where the unknown coefficients are
Substituting equations (1E,2E) and
Putting the above in normal form gives
Setting the numerator to zero gives
Looking at the above PDE shows the following are all the terms with
The following substitution is now made to be able to collect on
all terms with
The above PDE (6E) now becomes
Collecting the above on the terms
Equation (7E) now becomes
Setting each coefficients in (8E) to zero gives the following equations to solve
Solving the above equations for the unknowns gives
Substituting the above solution in the anstaz (1E,2E) (using
Shifting is now applied to make
The next step is to determine the canonical coordinates
The characteristic pde which is used to find the canonical coordinates is
The above comes from the requirements that
Which results in
Now that
Where in the above
Evaluating all the partial derivatives gives
Substituting all the above in (2) and simplifying gives the ode in canonical coordinates.
We now need to express the RHS as function of
The above is a quadrature ode. This is the whole point of Lie symmetry method. It converts an ode, no matter how complicated it is, to one that can be solved by integration when the ode is in the canonical coordiates
Since the ode has the form
To complete the solution, we just need to transform the above back to
The following diagram shows solution curves of the original ode and how they transform in the canonical coordinates space using the mapping shown.
Original ode in |
Canonical coordinates transformation |
ODE in canonical coordinates |
|
|
|
|
|
|
|
||
|
Solving for
Which simplifies to
Summary of solutions found
Time used: 0.130 (sec)
Solve
Let
Solving for
This has the form
Where
Taking derivative of (*) w.r.t.
Comparing the form
Hence (2) becomes
The singular solution is found by setting
Solving the above for
Substituting these in (1A) and keeping singular solution that verifies the ode gives
The general solution is found when
This ODE is now solved for
The ode
is separable as it can be written as
Where
Integrating gives
Taking the exponential of both sides the solution becomes
We now need to find the singular solutions, these are found by finding for what values
for
Now we go over each such singular solution and check if it verifies the ode itself and any initial conditions given. If it does not then the singular solution will not be used.
Therefore the solutions found are
Substituing the above solution for
Which simplifies to
Summary of solutions found
ode:=2*t+3*x(t)+(x(t)+2)*diff(x(t),t) = 0; dsolve(ode,x(t), singsol=all);
Maple trace
Methods for first order ODEs: --- Trying classification methods --- trying a quadrature trying 1st order linear trying Bernoulli trying separable trying inverse linear trying homogeneous types: trying homogeneous C trying homogeneous types: trying homogeneous D <- homogeneous successful <- homogeneous successful
Maple step by step
ode=2*t+3*x[t]+(x[t]+2)*D[x[t],t]==0; ic={}; DSolve[{ode,ic},x[t],t,IncludeSingularSolutions->True]
from sympy import * t = symbols("t") x = Function("x") ode = Eq(2*t + (x(t) + 2)*Derivative(x(t), t) + 3*x(t),0) ics = {} dsolve(ode,func=x(t),ics=ics)