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I would be thankful to anyone who can present an analytical solution to the following inhomogeneous PDE equation:

$$\frac{\partial{u}}{\partial{t}}= \alpha\frac{\partial^2{u}}{\partial{x^2}}-ku$$

$$u(0,t) = 0$$

$$u(1,t) = M_R$$

$$u(x,0) = x*f(x)$$

where k, $\alpha$ and $M_R$ are constants and k>0.

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    $\begingroup$ Hint: Fourier transform the thing $\endgroup$
    – user69109
    Commented Dec 3, 2019 at 18:11

1 Answer 1

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Set first $u= ve^{-kt}$ so that $ \partial_t u+ku=e^{-kt}(\partial_t v-kv+kv)=e^{-kt}\partial_t v. $ The equation becomes $$ \partial_t v=\alpha\partial_x^2 v, \quad v(0,t)=0, \quad v(1,t)=M_R e^{kt}, \quad v(x,0)=x\ast f(x). $$ You may assume $\alpha =1$ by writing $v(x,t)=w(x, \alpha t)$ and get then $$ \partial_t w=\partial_x^2 w, \quad w(0,t)=0, \quad w(1,t)=M_R e^{kt/\alpha}, \quad w(x,0)=x\ast f(x), $$ ending-up with an Initial-value and boundary problem for the heat equation. You can follow the standard Fourier method by looking for $2$-periodic functions in the variable $x$.

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  • $\begingroup$ Thank you so much Bazin. By Fourier method you mean separation of variables method which ends up with Fourier transform? if not would you please introduce a good reference which explains Fourier method? $\endgroup$ Commented Dec 14, 2019 at 4:07
  • $\begingroup$ For before you set $$v(x,t)=w(x, \alpha t)$$, I found a solution to find $$v(x,t)$$ at page 6 in: . people.maths.bris.ac.uk/~mazvs/supplementary.pdf $\endgroup$ Commented Dec 14, 2019 at 15:08

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