Internal
problem
ID
[3955] Book
:
Ordinary
differential
equations
and
their
solutions.
By
George
Moseley
Murphy.
1960 Section
:
Various
2 Problem
number
:
41 Date
solved
:
Thursday, October 17, 2024 at 11:46:33 AM CAS
classification
:
[_Riccati]
Solve
\begin{align*} y^{\prime }+1-x&=\left (x +y\right ) y \end{align*}
2.16.1 Solved as first order ode of type Riccati
Time used: 0.405 (sec)
In canonical form the ODE is
\begin{align*} y' &= F(x,y)\\ &= y x +y^{2}+x -1 \end{align*}
This is a Riccati ODE. Comparing the ODE to solve
\[ y' = y x +y^{2}+x -1 \]
With Riccati ODE standard form
\[ y' = f_0(x)+ f_1(x)y+f_2(x)y^{2} \]
Shows that \(f_0(x)=x -1\), \(f_1(x)=x\) and \(f_2(x)=1\). Let
Equation (7) is now solved. After finding \(z(x)\) then \(u\) is found using the inverse transformation
\begin{align*} u &= z \left (x \right ) e^{-\int \frac {B}{2 A} \,dx} \end{align*}
The first step is to determine the case of Kovacic algorithm this ode belongs to. There are 3
cases depending on the order of poles of \(r\) and the order of \(r\) at \(\infty \). The following table
summarizes these cases.
Need to have at least one pole
that is either order \(2\) or odd order
greater than \(2\). Any other pole order
is allowed as long as the above
condition is satisfied. Hence the
following set of pole orders are all
allowed. \(\{1,2\}\),\(\{1,3\}\),\(\{2\}\),\(\{3\}\),\(\{3,4\}\),\(\{1,2,5\}\).
no condition
3
\(\left \{ 1,2\right \} \)
\(\left \{ 2,3,4,5,6,7,\cdots \right \} \)
Table 1: Necessary conditions for each Kovacic case
The order of \(r\) at \(\infty \) is the degree of \(t\) minus the degree of \(s\). Therefore
There are no poles in \(r\). Therefore the set of poles \(\Gamma \) is empty. Since there is no odd order pole
larger than \(2\) and the order at \(\infty \) is \(-2\) then the necessary conditions for case one are met.
Therefore
\begin{align*} L &= [1] \end{align*}
Attempting to find a solution using case \(n=1\).
Since the order of \(r\) at \(\infty \) is \(O_r(\infty ) = -2\) then
Now we need to find \(b\), where \(b\) be the coefficient of \(x^{v-1} = x^{0}=1\) in \(r\) minus the coefficient of same term but
in \(\left ( [\sqrt r]_\infty \right )^2 \) where \([\sqrt r]_\infty \) was found above in Eq (10). Hence
This shows that the coefficient of \(1\) in the
above is \(1\). Now we need to find the coefficient of \(1\) in \(r\). How this is done depends on if \(v=0\) or
not. Since \(v=1\) which is not zero, then starting \(r=\frac {s}{t}\), we do long division and write this
in the form
\[ r = Q + \frac {R}{t} \]
Where \(Q\) is the quotient and \(R\) is the remainder. Then the coefficient
of \(1\) in \(r\) will be the coefficient this term in the quotient. Doing long division gives
The following table summarizes the findings so far for poles and for the order of \(r\) at \(\infty \) where \(r\)
is
\[ r=\frac {1}{4} x^{2}-x +\frac {1}{2} \]
Order of \(r\) at \(\infty \)
\([\sqrt r]_\infty \)
\(\alpha _\infty ^{+}\)
\(\alpha _\infty ^{-}\)
\(-2\)
\(\frac {x}{2}-1\)
\(-1\)
\(0\)
Now that the all \([\sqrt r]_c\) and its associated \(\alpha _c^{\pm }\) have been determined for all the poles in the set \(\Gamma \) and \([\sqrt r]_\infty \)
and its associated \(\alpha _\infty ^{\pm }\) have also been found, the next step is to determine possible non negative
integer \(d\) from these using
Where \(s(c)\) is either \(+\) or \(-\) and \(s(\infty )\) is the sign of \(\alpha _\infty ^{\pm }\). This is done by trial over all set of families \(s=(s(c))_{c \in \Gamma \cup {\infty }}\) until
such \(d\) is found to work in finding candidate \(\omega \). Trying \(\alpha _\infty ^{-} = 0\), and since there are no poles then
\begin{align*} d &= \alpha _\infty ^{-} \\ &= 0 \end{align*}
Since \(d\) an integer and \(d \geq 0\) then it can be used to find \(\omega \) using
Now that \(\omega \) is determined, the next step is find a corresponding minimal polynomial \(p(x)\) of degree
\(d=0\) to solve the ode. The polynomial \(p(x)\) needs to satisfy the equation
`Methodsfor first order ODEs:---Trying classification methods ---tryinga quadraturetrying1st order lineartryingBernoullitryingseparabletryinginverse lineartryinghomogeneous types:tryingChinidifferentialorder: 1; looking for linear symmetriestryingexactLookingfor potential symmetriestryingRiccatitryingRiccati sub-methods:<- Riccati particular polynomial solution successful`