## Solve heat equation in semi-infinite bounds with mathematica

How can I solve this in mathematica?$$u_t=Du_{xx}$$With the conditions:$$u(x,0)=u_0$$$$u(0,t)=u_s$$$$u(\infty,t)=u_0$$

I can't figure out how to input the infinite bound to work in DSolve or NDSolve.

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