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4.3 The Finite Element Method     continued...

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.