k = 1

k = 5

Mesh

Error

Order

Mesh

Error

Order

40 × 40

0.0022

40 × 40

0.0031

80 × 80

3.0955e−04

3.9638

80 × 80

3.2997e−04

3.4655

160 × 160

4.4832e−05

3.9914

160 × 160

2.7878e−05

3.6936

320 × 320

7.0240e−06

3.9982

320 × 320

1.9181e−06

3.9310

640 × 640

4.1684e−09

3.9997

640 × 640

1.2417e−07

3.9849