Solutions at the interior points
    P(1)      P(2)      P(3)     Computed    Exact
    0.5000    0.0000    0.0000    0.5179    0.5000
    0.0000    0.0000    0.2500    0.2935    0.2500
    0.0000    0.0000    0.5000    0.5245    0.5000
    0.0000    0.0000    0.7500    0.7622    0.7500