Hi, I have a problem trying to solve a differentail equation:

neff2a[x_] =  Piecewise[{{0.0, x <= zero}, {neff2[x][[2, 1, 2, 1]],   zero < x < d}, {0.0, x >= d}}]

where neff2[x] element is a constant value, so it is a step function:

.

I define differential equation:

ps2 = D[D[V2[x], x], x] == neff2a[x]/\[Kappa]

So it is defined like that:

I'm trying to solve the equation:

psres2 = NDSolve[{ps2, V2[0] == 0.0, V2[d] == U}, V2[x], {x, 0.0, d}]

but I get:

NDSolve::bvdisc: NDSolve is not currently able to solve boundary value problems with discrete variables. >>

why? Is there any way to solve this equation by Mathematica?

Thanks in advance, Mariusz