Internal problem ID [6491]
Internal file name [OUTPUT/5739_Sunday_June_05_2022_03_52_03_PM_28503853/index.tex]
Book: Differential Equations: Theory, Technique, and Practice by George Simmons, Steven
Krantz. McGraw-Hill NY. 2007. 1st Edition.
Section: Chapter 4. Power Series Solutions and Special Functions. Problems for review and
discovert. (A) Drill Exercises . Page 194
Problem number: 2(h).
ODE order: 2.
ODE degree: 1.
The type(s) of ODE detected by this program : "second order series method. Regular singular point. Repeated root"
Maple gives the following as the ode type
[[_2nd_order, _exact, _linear, _homogeneous]]
\[ \boxed {x y^{\prime \prime }+\left (x +1\right ) y^{\prime }+y=0} \] With the expansion point for the power series method at \(x = 0\).
The type of the expansion point is first determined. This is done on the homogeneous part of the ODE. \[ x y^{\prime \prime }+\left (x +1\right ) y^{\prime }+y = 0 \] The following is summary of singularities for the above ode. Writing the ode as \begin {align*} y^{\prime \prime }+p(x) y^{\prime } + q(x) y &=0 \end {align*}
Where \begin {align*} p(x) &= \frac {x +1}{x}\\ q(x) &= \frac {1}{x}\\ \end {align*}
Combining everything together gives the following summary of singularities for the ode as
Regular singular points : \([0]\)
Irregular singular points : \([\infty ]\)
Since \(x = 0\) is regular singular point, then Frobenius power series is used. The ode is normalized to be \[ x y^{\prime \prime }+\left (x +1\right ) y^{\prime }+y = 0 \] Let the solution be represented as Frobenius power series of the form \[ y = \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r} \] Then \begin{align*} y^{\prime } &= \moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1} \\ y^{\prime \prime } &= \moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) \left (n +r -1\right ) a_{n} x^{n +r -2} \\ \end{align*} Substituting the above back into the ode gives \begin{equation} \tag{1} x \left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) \left (n +r -1\right ) a_{n} x^{n +r -2}\right )+\left (x +1\right ) \left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1}\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r}\right ) = 0 \end{equation} Which simplifies to \begin{equation} \tag{2A} \left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r -1} a_{n} \left (n +r \right ) \left (n +r -1\right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r} a_{n} \left (n +r \right )\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1}\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r}\right ) = 0 \end{equation} The next step is to make all powers of \(x\) be \(n +r -1\) in each summation term. Going over each summation term above with power of \(x\) in it which is not already \(x^{n +r -1}\) and adjusting the power and the corresponding index gives \begin{align*} \moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r} a_{n} \left (n +r \right ) &= \moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) x^{n +r -1} \\ \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r} &= \moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} x^{n +r -1} \\ \end{align*} Substituting all the above in Eq (2A) gives the following equation where now all powers of \(x\) are the same and equal to \(n +r -1\). \begin{equation} \tag{2B} \left (\moverset {\infty }{\munderset {n =0}{\sum }}x^{n +r -1} a_{n} \left (n +r \right ) \left (n +r -1\right )\right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} \left (n +r -1\right ) x^{n +r -1}\right )+\left (\moverset {\infty }{\munderset {n =0}{\sum }}\left (n +r \right ) a_{n} x^{n +r -1}\right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}a_{n -1} x^{n +r -1}\right ) = 0 \end{equation} The indicial equation is obtained from \(n = 0\). From Eq (2B) this gives \[ x^{n +r -1} a_{n} \left (n +r \right ) \left (n +r -1\right )+\left (n +r \right ) a_{n} x^{n +r -1} = 0 \] When \(n = 0\) the above becomes \[ x^{-1+r} a_{0} r \left (-1+r \right )+r a_{0} x^{-1+r} = 0 \] Or \[ \left (x^{-1+r} r \left (-1+r \right )+r \,x^{-1+r}\right ) a_{0} = 0 \] Since \(a_{0}\neq 0\) then the above simplifies to \[ x^{-1+r} r^{2} = 0 \] Since the above is true for all \(x\) then the indicial equation becomes \[ r^{2} = 0 \] Solving for \(r\) gives the roots of the indicial equation as \begin {align*} r_1 &= 0\\ r_2 &= 0 \end {align*}
Since \(a_{0}\neq 0\) then the indicial equation becomes \[ x^{-1+r} r^{2} = 0 \] Solving for \(r\) gives the roots of the indicial equation as \([0, 0]\).
Since the root of the indicial equation is repeated, then we can construct two linearly independent solutions. The first solution has the form \begin {align*} y_{1}\left (x \right ) &= \moverset {\infty }{\munderset {n =0}{\sum }}a_{n} x^{n +r}\tag {1A} \end {align*}
Now the second solution \(y_{2}\) is found using \begin {align*} y_{2}\left (x \right ) &= y_{1}\left (x \right ) \ln \left (x \right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}b_{n} x^{n +r}\right )\tag {1B} \end {align*}
Then the general solution will be \[ y = c_{1} y_{1}\left (x \right )+c_{2} y_{2}\left (x \right ) \] In Eq (1B) the sum starts from 1 and not zero. In Eq (1A), \(a_{0}\) is never zero, and is arbitrary and is typically taken as \(a_{0} = 1\), and \(\{c_{1}, c_{2}\}\) are two arbitray constants of integration which can be found from initial conditions. We start by finding the first solution \(y_{1}\left (x \right )\). Eq (2B) derived above is now used to find all \(a_{n}\) coefficients. The case \(n = 0\) is skipped since it was used to find the roots of the indicial equation. \(a_{0}\) is arbitrary and taken as \(a_{0} = 1\). For \(1\le n\) the recursive equation is \begin{equation} \tag{3} a_{n} \left (n +r \right ) \left (n +r -1\right )+a_{n -1} \left (n +r -1\right )+a_{n} \left (n +r \right )+a_{n -1} = 0 \end{equation} Solving for \(a_{n}\) from recursive equation (4) gives \[ a_{n} = -\frac {a_{n -1}}{n +r}\tag {4} \] Which for the root \(r = 0\) becomes \[ a_{n} = -\frac {a_{n -1}}{n}\tag {5} \] At this point, it is a good idea to keep track of \(a_{n}\) in a table both before substituting \(r = 0\) and after as more terms are found using the above recursive equation.
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
For \(n = 1\), using the above recursive equation gives \[ a_{1}=-\frac {1}{1+r} \] Which for the root \(r = 0\) becomes \[ a_{1}=-1 \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
For \(n = 2\), using the above recursive equation gives \[ a_{2}=\frac {1}{\left (1+r \right ) \left (2+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{2}={\frac {1}{2}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
For \(n = 3\), using the above recursive equation gives \[ a_{3}=-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{3}=-{\frac {1}{6}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
| \(a_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) |
For \(n = 4\), using the above recursive equation gives \[ a_{4}=\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{4}={\frac {1}{24}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
| \(a_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) |
| \(a_{4}\) | \(\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(\frac {1}{24}\) |
For \(n = 5\), using the above recursive equation gives \[ a_{5}=-\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{5}=-{\frac {1}{120}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
| \(a_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) |
| \(a_{4}\) | \(\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(\frac {1}{24}\) |
| \(a_{5}\) | \(-\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{120}}\) |
For \(n = 6\), using the above recursive equation gives \[ a_{6}=\frac {1}{\left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{6}={\frac {1}{720}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
| \(a_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) |
| \(a_{4}\) | \(\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(\frac {1}{24}\) |
| \(a_{5}\) | \(-\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{120}}\) |
| \(a_{6}\) | \(\frac {1}{\left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(\frac {1}{720}\) |
For \(n = 7\), using the above recursive equation gives \[ a_{7}=-\frac {1}{\left (7+r \right ) \left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )} \] Which for the root \(r = 0\) becomes \[ a_{7}=-{\frac {1}{5040}} \] And the table now becomes
| \(n\) | \(a_{n ,r}\) | \(a_{n}\) |
| \(a_{0}\) | \(1\) | \(1\) |
| \(a_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) |
| \(a_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) |
| \(a_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) |
| \(a_{4}\) | \(\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(\frac {1}{24}\) |
| \(a_{5}\) | \(-\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{120}}\) |
| \(a_{6}\) | \(\frac {1}{\left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(\frac {1}{720}\) |
| \(a_{7}\) | \(-\frac {1}{\left (7+r \right ) \left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{5040}}\) |
Using the above table, then the first solution \(y_{1}\left (x \right )\) becomes \begin{align*} y_{1}\left (x \right )&= a_{0}+a_{1} x +a_{2} x^{2}+a_{3} x^{3}+a_{4} x^{4}+a_{5} x^{5}+a_{6} x^{6}+a_{7} x^{7}+a_{8} x^{8}\dots \\ &= 1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right ) \\ \end{align*} Now the second solution is found. The second solution is given by \[ y_{2}\left (x \right ) = y_{1}\left (x \right ) \ln \left (x \right )+\left (\moverset {\infty }{\munderset {n =1}{\sum }}b_{n} x^{n +r}\right ) \] Where \(b_{n}\) is found using \[ b_{n} = \frac {d}{d r}a_{n ,r} \] And the above is then evaluated at \(r = 0\). The above table for \(a_{n ,r}\) is used for this purpose. Computing the derivatives gives the following table
| \(n\) | \(b_{n ,r}\) | \(a_{n}\) | \(b_{n ,r} = \frac {d}{d r}a_{n ,r}\) | \(b_{n}\left (r =0\right )\) |
| \(b_{0}\) | \(1\) | \(1\) | N/A since \(b_{n}\) starts from 1 | N/A |
| \(b_{1}\) | \(-\frac {1}{1+r}\) | \(-1\) | \(\frac {1}{\left (1+r \right )^{2}}\) | \(1\) |
| \(b_{2}\) | \(\frac {1}{\left (1+r \right ) \left (2+r \right )}\) | \(\frac {1}{2}\) | \(\frac {-3-2 r}{\left (1+r \right )^{2} \left (2+r \right )^{2}}\) | \(-{\frac {3}{4}}\) |
| \(b_{3}\) | \(-\frac {1}{\left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(-{\frac {1}{6}}\) | \(\frac {3 r^{2}+12 r +11}{\left (1+r \right )^{2} \left (2+r \right )^{2} \left (3+r \right )^{2}}\) | \(\frac {11}{36}\) |
| \(b_{4}\) | \(\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right )}\) | \(\frac {1}{24}\) | \(\frac {-4 r^{3}-30 r^{2}-70 r -50}{\left (4+r \right )^{2} \left (1+r \right )^{2} \left (2+r \right )^{2} \left (3+r \right )^{2}}\) | \(-{\frac {25}{288}}\) |
| \(b_{5}\) | \(-\frac {1}{\left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{120}}\) | \(\frac {5 r^{4}+60 r^{3}+255 r^{2}+450 r +274}{\left (4+r \right )^{2} \left (1+r \right )^{2} \left (2+r \right )^{2} \left (3+r \right )^{2} \left (5+r \right )^{2}}\) | \(\frac {137}{7200}\) |
| \(b_{6}\) | \(\frac {1}{\left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(\frac {1}{720}\) | \(\frac {-6 r^{5}-105 r^{4}-700 r^{3}-2205 r^{2}-3248 r -1764}{\left (6+r \right )^{2} \left (4+r \right )^{2} \left (1+r \right )^{2} \left (2+r \right )^{2} \left (3+r \right )^{2} \left (5+r \right )^{2}}\) | \(-{\frac {49}{14400}}\) |
| \(b_{7}\) | \(-\frac {1}{\left (7+r \right ) \left (6+r \right ) \left (4+r \right ) \left (1+r \right ) \left (2+r \right ) \left (3+r \right ) \left (5+r \right )}\) | \(-{\frac {1}{5040}}\) | \(\frac {7 r^{6}+168 r^{5}+1610 r^{4}+7840 r^{3}+20307 r^{2}+26264 r +13068}{\left (7+r \right )^{2} \left (6+r \right )^{2} \left (4+r \right )^{2} \left (1+r \right )^{2} \left (2+r \right )^{2} \left (3+r \right )^{2} \left (5+r \right )^{2}}\) | \(\frac {121}{235200}\) |
The above table gives all values of \(b_{n}\) needed. Hence the second solution is \begin{align*} y_{2}\left (x \right )&=y_{1}\left (x \right ) \ln \left (x \right )+b_{0}+b_{1} x +b_{2} x^{2}+b_{3} x^{3}+b_{4} x^{4}+b_{5} x^{5}+b_{6} x^{6}+b_{7} x^{7}+b_{8} x^{8}\dots \\ &= \left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) \ln \left (x \right )+x -\frac {3 x^{2}}{4}+\frac {11 x^{3}}{36}-\frac {25 x^{4}}{288}+\frac {137 x^{5}}{7200}-\frac {49 x^{6}}{14400}+\frac {121 x^{7}}{235200}+O\left (x^{8}\right ) \\ \end{align*} Therefore the homogeneous solution is \begin{align*} y_h(x) &= c_{1} y_{1}\left (x \right )+c_{2} y_{2}\left (x \right ) \\ &= c_{1} \left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) + c_{2} \left (\left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) \ln \left (x \right )+x -\frac {3 x^{2}}{4}+\frac {11 x^{3}}{36}-\frac {25 x^{4}}{288}+\frac {137 x^{5}}{7200}-\frac {49 x^{6}}{14400}+\frac {121 x^{7}}{235200}+O\left (x^{8}\right )\right ) \\ \end{align*} Hence the final solution is \begin{align*} y &= y_h \\ &= c_{1} \left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right )+c_{2} \left (\left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) \ln \left (x \right )+x -\frac {3 x^{2}}{4}+\frac {11 x^{3}}{36}-\frac {25 x^{4}}{288}+\frac {137 x^{5}}{7200}-\frac {49 x^{6}}{14400}+\frac {121 x^{7}}{235200}+O\left (x^{8}\right )\right ) \\ \end{align*}
The solution(s) found are the following \begin{align*} \tag{1} y &= c_{1} \left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right )+c_{2} \left (\left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) \ln \left (x \right )+x -\frac {3 x^{2}}{4}+\frac {11 x^{3}}{36}-\frac {25 x^{4}}{288}+\frac {137 x^{5}}{7200}-\frac {49 x^{6}}{14400}+\frac {121 x^{7}}{235200}+O\left (x^{8}\right )\right ) \\ \end{align*}
Verification of solutions
\[ y = c_{1} \left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right )+c_{2} \left (\left (1-x +\frac {x^{2}}{2}-\frac {x^{3}}{6}+\frac {x^{4}}{24}-\frac {x^{5}}{120}+\frac {x^{6}}{720}-\frac {x^{7}}{5040}+O\left (x^{8}\right )\right ) \ln \left (x \right )+x -\frac {3 x^{2}}{4}+\frac {11 x^{3}}{36}-\frac {25 x^{4}}{288}+\frac {137 x^{5}}{7200}-\frac {49 x^{6}}{14400}+\frac {121 x^{7}}{235200}+O\left (x^{8}\right )\right ) \] Verified OK.
\[ \begin {array}{lll} & {} & \textrm {Let's solve}\hspace {3pt} \\ {} & {} & x \left (\frac {d}{d x}y^{\prime }\right )+\left (x +1\right ) y^{\prime }+y=0 \\ \bullet & {} & \textrm {Highest derivative means the order of the ODE is}\hspace {3pt} 2 \\ {} & {} & \frac {d}{d x}y^{\prime } \\ \bullet & {} & \textrm {Isolate 2nd derivative}\hspace {3pt} \\ {} & {} & \frac {d}{d x}y^{\prime }=-\frac {\left (x +1\right ) y^{\prime }}{x}-\frac {y}{x} \\ \bullet & {} & \textrm {Group terms with}\hspace {3pt} y\hspace {3pt}\textrm {on the lhs of the ODE and the rest on the rhs of the ODE; ODE is linear}\hspace {3pt} \\ {} & {} & \frac {d}{d x}y^{\prime }+\frac {\left (x +1\right ) y^{\prime }}{x}+\frac {y}{x}=0 \\ \square & {} & \textrm {Check to see if}\hspace {3pt} x_{0}=0\hspace {3pt}\textrm {is a regular singular point}\hspace {3pt} \\ {} & \circ & \textrm {Define functions}\hspace {3pt} \\ {} & {} & \left [P_{2}\left (x \right )=\frac {x +1}{x}, P_{3}\left (x \right )=\frac {1}{x}\right ] \\ {} & \circ & x \cdot P_{2}\left (x \right )\textrm {is analytic at}\hspace {3pt} x =0 \\ {} & {} & \left (x \cdot P_{2}\left (x \right )\right )\bigg | {\mstack {}{_{x \hiderel {=}0}}}=1 \\ {} & \circ & x^{2}\cdot P_{3}\left (x \right )\textrm {is analytic at}\hspace {3pt} x =0 \\ {} & {} & \left (x^{2}\cdot P_{3}\left (x \right )\right )\bigg | {\mstack {}{_{x \hiderel {=}0}}}=0 \\ {} & \circ & x =0\textrm {is a regular singular point}\hspace {3pt} \\ & {} & \textrm {Check to see if}\hspace {3pt} x_{0}=0\hspace {3pt}\textrm {is a regular singular point}\hspace {3pt} \\ {} & {} & x_{0}=0 \\ \bullet & {} & \textrm {Multiply by denominators}\hspace {3pt} \\ {} & {} & x \left (\frac {d}{d x}y^{\prime }\right )+\left (x +1\right ) y^{\prime }+y=0 \\ \bullet & {} & \textrm {Assume series solution for}\hspace {3pt} y \\ {} & {} & y=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} x^{k +r} \\ \square & {} & \textrm {Rewrite ODE with series expansions}\hspace {3pt} \\ {} & \circ & \textrm {Convert}\hspace {3pt} x^{m}\cdot y^{\prime }\hspace {3pt}\textrm {to series expansion for}\hspace {3pt} m =0..1 \\ {} & {} & x^{m}\cdot y^{\prime }=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} \left (k +r \right ) x^{k +r -1+m} \\ {} & \circ & \textrm {Shift index using}\hspace {3pt} k \mathrm {->}k +1-m \\ {} & {} & x^{m}\cdot y^{\prime }=\moverset {\infty }{\munderset {k =-1+m}{\sum }}a_{k +1-m} \left (k +1-m +r \right ) x^{k +r} \\ {} & \circ & \textrm {Convert}\hspace {3pt} x \cdot \left (\frac {d}{d x}y^{\prime }\right )\hspace {3pt}\textrm {to series expansion}\hspace {3pt} \\ {} & {} & x \cdot \left (\frac {d}{d x}y^{\prime }\right )=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} \left (k +r \right ) \left (k +r -1\right ) x^{k +r -1} \\ {} & \circ & \textrm {Shift index using}\hspace {3pt} k \mathrm {->}k +1 \\ {} & {} & x \cdot \left (\frac {d}{d x}y^{\prime }\right )=\moverset {\infty }{\munderset {k =-1}{\sum }}a_{k +1} \left (k +1+r \right ) \left (k +r \right ) x^{k +r} \\ & {} & \textrm {Rewrite ODE with series expansions}\hspace {3pt} \\ {} & {} & a_{0} r^{2} x^{-1+r}+\left (\moverset {\infty }{\munderset {k =0}{\sum }}\left (a_{k +1} \left (k +1+r \right )^{2}+a_{k} \left (k +1+r \right )\right ) x^{k +r}\right )=0 \\ \bullet & {} & a_{0}\textrm {cannot be 0 by assumption, giving the indicial equation}\hspace {3pt} \\ {} & {} & r^{2}=0 \\ \bullet & {} & \textrm {Values of r that satisfy the indicial equation}\hspace {3pt} \\ {} & {} & r =0 \\ \bullet & {} & \textrm {Each term in the series must be 0, giving the recursion relation}\hspace {3pt} \\ {} & {} & \left (k +1\right ) \left (a_{k +1} \left (k +1\right )+a_{k}\right )=0 \\ \bullet & {} & \textrm {Recursion relation that defines series solution to ODE}\hspace {3pt} \\ {} & {} & a_{k +1}=-\frac {a_{k}}{k +1} \\ \bullet & {} & \textrm {Recursion relation for}\hspace {3pt} r =0 \\ {} & {} & a_{k +1}=-\frac {a_{k}}{k +1} \\ \bullet & {} & \textrm {Solution for}\hspace {3pt} r =0 \\ {} & {} & \left [y=\moverset {\infty }{\munderset {k =0}{\sum }}a_{k} x^{k}, a_{k +1}=-\frac {a_{k}}{k +1}\right ] \end {array} \]
Maple trace
`Methods for second order ODEs: --- Trying classification methods --- trying a quadrature checking if the LODE has constant coefficients checking if the LODE is of Euler type trying a symmetry of the form [xi=0, eta=F(x)] <- linear_1 successful`
✓ Solution by Maple
Time used: 0.016 (sec). Leaf size: 71
Order:=8; dsolve(x*diff(y(x),x$2)+(x+1)*diff(y(x),x)+y(x)=0,y(x),type='series',x=0);
\[ y \left (x \right ) = \left (c_{2} \ln \left (x \right )+c_{1} \right ) \left (1-x +\frac {1}{2} x^{2}-\frac {1}{6} x^{3}+\frac {1}{24} x^{4}-\frac {1}{120} x^{5}+\frac {1}{720} x^{6}-\frac {1}{5040} x^{7}+\operatorname {O}\left (x^{8}\right )\right )+\left (x -\frac {3}{4} x^{2}+\frac {11}{36} x^{3}-\frac {25}{288} x^{4}+\frac {137}{7200} x^{5}-\frac {49}{14400} x^{6}+\frac {121}{235200} x^{7}+\operatorname {O}\left (x^{8}\right )\right ) c_{2} \]
✓ Solution by Mathematica
Time used: 0.005 (sec). Leaf size: 151
AsymptoticDSolveValue[x*y''[x]+(x+1)*y'[x]+y[x]==0,y[x],{x,0,7}]
\[ y(x)\to c_1 \left (-\frac {x^7}{5040}+\frac {x^6}{720}-\frac {x^5}{120}+\frac {x^4}{24}-\frac {x^3}{6}+\frac {x^2}{2}-x+1\right )+c_2 \left (\frac {121 x^7}{235200}-\frac {49 x^6}{14400}+\frac {137 x^5}{7200}-\frac {25 x^4}{288}+\frac {11 x^3}{36}-\frac {3 x^2}{4}+\left (-\frac {x^7}{5040}+\frac {x^6}{720}-\frac {x^5}{120}+\frac {x^4}{24}-\frac {x^3}{6}+\frac {x^2}{2}-x+1\right ) \log (x)+x\right ) \]