Differential equation

1. Sep 22, 2013

saidMath

Hello I seek solutions of differential equation

x3y′′(x)+(ax3+bx2+cx+d)y(x)=0

thank you

2. Sep 22, 2013

jackmell

Hi,

That's poorly formatted. But ok you're new. Try your best, if you want to ask other questions, to format it perfectly and to show some effort even if it's minor. So you're looking I think to solve:

$$x^3 y''+(ax^3+bx^2+cx+d) y=0$$

I used the math formatting code or Latex to format it. Do a quote on my post to see the code. We can write it as:

$$y''+(a+\frac{b}{x}+\frac{c}{x^2}+\frac{d}{x^3})y=0$$

Isn't 0 now an irregular singular point? In fact, it is having rank of 1/2. Until someone comes up with a better approach, let me make this suggestion that you probably won't like at all: Since the rank of the singular point is non-integer, let's for starters, work one with the smallest integer rank of k=1. In that case, we could look at the equation:

$$x^4 y''+(x^4+1)y=0$$

http://ocw.mit.edu/courses/mathemat...ngineering-fall-2004/lecture-notes/eight1.pdf

it deals with irregular singular points of rank one. Can we use that paper to solve this equation first? I realize that's taking a bunch of steps backwards but sometimes you have to bust down a lot of walls before you lay the first course. :)

May I ask that we change the title of this to "Solving a DE with an irregular singular point"? That would make it much more interesting.

Last edited: Sep 22, 2013
3. Sep 22, 2013

JJacquelin

Hi saidMath !
Do you known the hypergeometric functions ?
The equation x3y′′(x)+(ax3+bx2+cx+d)y(x)=0 requieres an high level of special functions.
Even with a simpler equation x2y′′(x)+(ax2+bx+c)y(x)=0, the solutions are expressed as a combination of confluent hypergeometric functions (Kummer and Tricomi functions).
Nevertheless, in some particular cases, with particular values of parameters a, b, c, d, the solutions can be reduced to functions of lower level.
So, the question is : are the parameters a, b, c, d resticted to some particular values ?
If not, do not expect to find the solutions in terms of a combination of a finite number of elementary functions and of usual special functions.