Furthermore, if satisfies (33), then we have [34]. Finally, since itself can be expressed as the linear combination:

we can then write (33) as:

subject to the Dirichlet boundary condition. Then the finite element approximation of (1) can equivalently be expressed as a system of N equations with N unknowns (the electrostatic potentials, for example). In matrix form, the above system can be written as , where is called the global stiffness matrix and has elements , while and is usually termed the load vector.