- #1
LukeMiller86
- 5
- 0
Use Green's Functions to solve:
[tex]\frac{d^{2}y}{dx^{2}} + y = cosec x[/tex]
Subject to the boundary conditions:
[tex]y\left(0\right) = y\left(\frac{\pi}{2}\right) = 0[/tex]
Attempt:
[tex]\frac{d^{2}G\left(x,z\right)}{dx^{2}} + G\left(x,z\right) = \delta\left(x-z\right)[/tex]
For [tex]x\neq z [/tex] the RHS is zero so the complementary solution consists of sinx and cosx terms but with different superpositions on either side of x = z since the first derivative is required to have a discontinuity there.
Assume a form [tex] G\left(x,z\right) = A\left(z\right)sinx + B\left(z\right)cosx [/tex] for x < z
and [tex]G\left(x,z\right) = C\left(z\right)sinx + D\left(z\right)cosx [/tex] for x > z
I'm just following an example from a book that then continues to state that according to the boundary conditions B and C are equal to zero, seems simple but I'm unclear as to how they achieve this. I don't see how to apply this and discern B and C being zero, I seem to just find A,B,C and D all zero. Also how would one proceed in the case of the boundary conditions stating G and its first derivative equal to zero and achieve A and B zero?
Cheers
[tex]\frac{d^{2}y}{dx^{2}} + y = cosec x[/tex]
Subject to the boundary conditions:
[tex]y\left(0\right) = y\left(\frac{\pi}{2}\right) = 0[/tex]
Attempt:
[tex]\frac{d^{2}G\left(x,z\right)}{dx^{2}} + G\left(x,z\right) = \delta\left(x-z\right)[/tex]
For [tex]x\neq z [/tex] the RHS is zero so the complementary solution consists of sinx and cosx terms but with different superpositions on either side of x = z since the first derivative is required to have a discontinuity there.
Assume a form [tex] G\left(x,z\right) = A\left(z\right)sinx + B\left(z\right)cosx [/tex] for x < z
and [tex]G\left(x,z\right) = C\left(z\right)sinx + D\left(z\right)cosx [/tex] for x > z
I'm just following an example from a book that then continues to state that according to the boundary conditions B and C are equal to zero, seems simple but I'm unclear as to how they achieve this. I don't see how to apply this and discern B and C being zero, I seem to just find A,B,C and D all zero. Also how would one proceed in the case of the boundary conditions stating G and its first derivative equal to zero and achieve A and B zero?
Cheers