Need to Compute Intermediate solutions of Heat equation

General Discussion
1

Hello, all experts, i have applied backward-Euler in Time dependent Heat equation. I am getting good results also. I want to store the intermediate solutions u^{1}, u^{2},…,u^{n-1}, where u^0 is the initial solution and u^{n} is the final solution. Then, i want to compute an expression:

Blockquote
X=exp(-a*(n-1)*dt)u_{1}+exp(-a(n-2)*dt)u_{2}+…+exp(-adt)*u_{n-1}
Blockquote
, where n comes from space refinement loop and dt is time step (known), a=0.1(known). u^{1}, u^{2},…,u^{n-1} are all knowns intermediate solutions of Heat equations.
Here, is my Code.
Heat.edp (2.2 KB)

Thanks in advance.