fem_check_abc_la.c running 
Given a1 uxx + b1 uxy + c1 uyy + d1 ux + e1 uy + f1 u = 
c(x,y) 
xmin<=x<=xmax ymin<=y<=ymax Boundaries 
Analytic solution u(x) =  
xmin=-1, xmax=1, ymin=-1, ymax=1 
nx=6, ny=5 
x grid and analytic solution at ymin 
i=0, Ua(-1.000)=-10.000 
i=1, Ua(-0.600)=-5.296 
i=2, Ua(-0.200)=-2.128 
i=3, Ua( 0.200)=-0.112 
i=4, Ua( 0.600)= 1.136 
i=5, Ua( 1.000)= 2.000 

y grid and analytic solution at xmin
ii=0, Ua(-1.000)=-10.000 
ii=1, Ua(-0.500)=-2.750 
ii=2, Ua( 0.000)= 1.000 
ii=3, Ua( 0.500)= 2.750 
ii=4, Ua( 1.000)= 4.000 

solution at i=0,x=-1, ii=0,y=-1 is -10 
solution at i=0,x=-1, ii=1,y=-0.5 is -2.75 
solution at i=0,x=-1, ii=2,y=0 is 1 
solution at i=0,x=-1, ii=3,y=0.5 is 2.75 
solution at i=0,x=-1, ii=4,y=1 is 4 
solution at i=1,x=-0.6, ii=0,y=-1 is -5.296 
solution at i=1,x=-0.6, ii=1,y=-0.5 is 0.794 
solution at i=1,x=-0.6, ii=2,y=0 is 4.184 
solution at i=1,x=-0.6, ii=3,y=0.5 is 6.374 
solution at i=1,x=-0.6, ii=4,y=1 is 8.864 
solution at i=2,x=-0.2, ii=0,y=-1 is -2.128 
solution at i=2,x=-0.2, ii=1,y=-0.5 is 3.282 
solution at i=2,x=-0.2, ii=2,y=0 is 6.792 
solution at i=2,x=-0.2, ii=3,y=0.5 is 9.902 
solution at i=2,x=-0.2, ii=4,y=1 is 14.112 
solution at i=3,x=0.2, ii=0,y=-1 is -0.112 
solution at i=3,x=0.2, ii=1,y=-0.5 is 5.098 
solution at i=3,x=0.2, ii=2,y=0 is 9.208 
solution at i=3,x=0.2, ii=3,y=0.5 is 13.718 
solution at i=3,x=0.2, ii=4,y=1 is 20.128 
solution at i=4,x=0.6, ii=0,y=-1 is 1.136 
solution at i=4,x=0.6, ii=1,y=-0.5 is 6.626 
solution at i=4,x=0.6, ii=2,y=0 is 11.816 
solution at i=4,x=0.6, ii=3,y=0.5 is 18.206 
solution at i=4,x=0.6, ii=4,y=1 is 27.296 
solution at i=5,x=1, ii=0,y=-1 is 2 
solution at i=5,x=1, ii=1,y=-0.5 is 8.25 
solution at i=5,x=1, ii=2,y=0 is 15 
solution at i=5,x=1, ii=3,y=0.5 is 23.75 
solution at i=5,x=1, ii=4,y=1 is 36 

boundary i=0,x=-1, ii=0,y=-1 is -10 
boundary i=0,x=-1, ii=4,y=1 is 4 
boundary i=1,x=-0.6, ii=0,y=-1 is -5.296 
boundary i=1,x=-0.6, ii=4,y=1 is 8.864 
boundary i=2,x=-0.2, ii=0,y=-1 is -2.128 
boundary i=2,x=-0.2, ii=4,y=1 is 14.112 
boundary i=3,x=0.2, ii=0,y=-1 is -0.112 
boundary i=3,x=0.2, ii=4,y=1 is 20.128 
boundary i=4,x=0.6, ii=0,y=-1 is 1.136 
boundary i=4,x=0.6, ii=4,y=1 is 27.296 
boundary i=5,x=1, ii=0,y=-1 is 2 
boundary i=5,x=1, ii=4,y=1 is 36 
boundary i=0,x=-1, ii=0,y=-1 is -10 
boundary i=5,x=1, ii=0,y=-1 is 2 
boundary i=0,x=-1, ii=1,y=-0.5 is -2.75 
boundary i=5,x=1, ii=1,y=-0.5 is 8.25 
boundary i=0,x=-1, ii=2,y=0 is 1 
boundary i=5,x=1, ii=2,y=0 is 15 
boundary i=0,x=-1, ii=3,y=0.5 is 2.75 
boundary i=5,x=1, ii=3,y=0.5 is 23.75 
boundary i=0,x=-1, ii=4,y=1 is 4 
boundary i=5,x=1, ii=4,y=1 is 36 
calling gauleg xmin=-1, xmax=1, npx=48 
calling gauleg ymin=-1, ymax=1, npy=48 
compute stiffness matrix 
ug computed Galerkin, Ua analytic, error 
ug[0,0]=-10.000, Ua=-10.000, err=1.77636e-15 
ug[0,1]=-2.750, Ua=-2.750, err=1.5099e-14 
ug[0,2]= 1.000, Ua= 1.000, err=3.55271e-15 
ug[0,3]= 2.750, Ua= 2.750, err=0 
ug[0,4]= 4.000, Ua= 4.000, err=0 
ug[1,0]=-5.296, Ua=-5.296, err=8.88178e-16 
ug[1,1]= 0.794, Ua= 0.794, err=3.05311e-14 
ug[1,2]= 4.184, Ua= 4.184, err=2.75335e-14 
ug[1,3]= 6.374, Ua= 6.374, err=1.68754e-14 
ug[1,4]= 8.864, Ua= 8.864, err=1.77636e-15 
ug[2,0]=-2.128, Ua=-2.128, err=2.66454e-15 
ug[2,1]= 3.282, Ua= 3.282, err=5.10703e-14 
ug[2,2]= 6.792, Ua= 6.792, err=7.28306e-14 
ug[2,3]= 9.902, Ua= 9.902, err=4.44089e-14 
ug[2,4]=14.112, Ua=14.112, err=-3.55271e-15 
ug[3,0]=-0.112, Ua=-0.112, err=-2.55351e-15 
ug[3,1]= 5.098, Ua= 5.098, err=5.41789e-14 
ug[3,2]= 9.208, Ua= 9.208, err=1.13687e-13 
ug[3,3]=13.718, Ua=13.718, err=6.57252e-14 
ug[3,4]=20.128, Ua=20.128, err=0 
ug[4,0]= 1.136, Ua= 1.136, err=4.21885e-15 
ug[4,1]= 6.626, Ua= 6.626, err=6.30607e-14 
ug[4,2]=11.816, Ua=11.816, err=1.04805e-13 
ug[4,3]=18.206, Ua=18.206, err=4.9738e-14 
ug[4,4]=27.296, Ua=27.296, err=0 
ug[5,0]= 2.000, Ua= 2.000, err=0 
ug[5,1]= 8.250, Ua= 8.250, err=0 
ug[5,2]=15.000, Ua=15.000, err=0 
ug[5,3]=23.750, Ua=23.750, err=0 
ug[5,4]=36.000, Ua=36.000, err=0 
                                        maxerr=1.13687e-13, avgerr=2.43509e-14 
end fem_check_abc_la.c