- #1
Judas503
- 23
- 0
I'm seeking the solution to the following integro-differential equation:
$$ \frac{\partial c(x,t)}{\partial t}=-xc(x,t)+2\int_{x}^{\infty} c(y,t)dy$$
I know that to solve this, the Laplace transform must be taken term by term. Let
$$ \mathcal{L}\{c(x,t)\}=\int_{0}^{\infty}e^{-st}c(x,s) $$
Then, $$ \mathcal{L}\{ \frac{\partial c(x,t)}{\partial t} \}=s\mathcal{L}\{c(x,t)\}-c(x,0)$$
and, $$ \mathcal{L}\{xc(x,t)\}=x\mathcal{L}\{c(x,t)\} $$
The problem arises with the Laplace transform of the integral.
\begin{align*}
\mathcal{L}\{ \int_{x}^{\infty}c(y,t)dt \} &= \mathcal{L}\{ \int_{0}^{\infty}c(y,t)dt \}-\mathcal{L}\{ \int_{0}^{x}c(y,t)dt \}
\\&=\mathcal{L}\{ \int_{0}^{\infty}c(y,t)dt \}-\frac{\mathcal{L}\{ c(x,t) \}}{s}
\end{align*}
My question is what do I do with the first integral of the last equation?
$$ \frac{\partial c(x,t)}{\partial t}=-xc(x,t)+2\int_{x}^{\infty} c(y,t)dy$$
I know that to solve this, the Laplace transform must be taken term by term. Let
$$ \mathcal{L}\{c(x,t)\}=\int_{0}^{\infty}e^{-st}c(x,s) $$
Then, $$ \mathcal{L}\{ \frac{\partial c(x,t)}{\partial t} \}=s\mathcal{L}\{c(x,t)\}-c(x,0)$$
and, $$ \mathcal{L}\{xc(x,t)\}=x\mathcal{L}\{c(x,t)\} $$
The problem arises with the Laplace transform of the integral.
\begin{align*}
\mathcal{L}\{ \int_{x}^{\infty}c(y,t)dt \} &= \mathcal{L}\{ \int_{0}^{\infty}c(y,t)dt \}-\mathcal{L}\{ \int_{0}^{x}c(y,t)dt \}
\\&=\mathcal{L}\{ \int_{0}^{\infty}c(y,t)dt \}-\frac{\mathcal{L}\{ c(x,t) \}}{s}
\end{align*}
My question is what do I do with the first integral of the last equation?