Change of variables in Seocnd order ODES

phil ess
Messages
67
Reaction score
0
I am looking through my course notes for mathematical physics, in preparation for the exam, and I've run into a concept that I can't figure out. It comes up first when talking about the modified bessel's equation

(x^2)y''+(x)y'-(x^2+p^2)y=0

And supposedly this can be transformed into bessel's euqation by using the substitution t=ix, but I can't figure out how this works. This is just the specific example that this issue came up in; I don't understand generally how to perform a change of variables for second order equations.

I start with dt=idx and -t^2=x^2, but how do I deal with y'' and y'?

If anyone can explain how change of variables works to me it would be greatly appreciated!
 
Physics news on Phys.org
dt = i dx
dx = -i dt

dy/dx = dy/(-i dt) = i dy/dt

d²y/dx² = d(dy/dx)/dx = d(i dy/dt) / (-i dt) = - d²y/dt²
 
Thread 'Direction Fields and Isoclines'
I sketched the isoclines for $$ m=-1,0,1,2 $$. Since both $$ \frac{dy}{dx} $$ and $$ D_{y} \frac{dy}{dx} $$ are continuous on the square region R defined by $$ -4\leq x \leq 4, -4 \leq y \leq 4 $$ the existence and uniqueness theorem guarantees that if we pick a point in the interior that lies on an isocline there will be a unique differentiable function (solution) passing through that point. I understand that a solution exists but I unsure how to actually sketch it. For example, consider a...

Similar threads

Back
Top