will solve a simple version of Poisson's equation with zero boundary
values, but a nonzero right hand side:
@f{align*}
- -\Delta u &= 1 \qquad\qquad & \text{in}\ \Omega,
+ -\Delta u &= f \qquad\qquad & \text{in}\ \Omega,
\\
u &= 0 \qquad\qquad & \text{on}\ \partial\Omega.
@f}
We will solve this equation on the unit square, $\Omega=[0,1]^2$, for which
-you've already learned how to generate a mesh in step-1 and step-2.
+you've already learned how to generate a mesh in step-1 and step-2. In
+this program, we will also only consider the particular case
+$f(\mathbf x)=1$ and come back to how to implement the more general
+case in the next tutorial program, step-4.
If you've learned about the basics of the finite element method, you will
remember the steps we need to take to approximate the solution $u$ by a finite