$J$

®

8

16

32

64

${\Vert grad\left(u-u_h\right)\Vert }_h$

®

0.143615 E−2

0.367543 E−3

0.927840 E−4

0.232998 E−4

${\Vert u-u_h\Vert }_h$

®

0.183918 E−4

0.230310 E−5

0.289312 E−6

0.363247 E−7

$max\left|u-u_h\right|$ at the nodes

®

0.172473 E−2

0.446493 E−3

0.112615 E−3

0.282163 E−4