您可以将解决方案插入到更精细的网格上，然后绘制它：

from dolfin import *

coarse_mesh = UnitSquareMesh(2, 2)
fine_mesh = refine(refine(refine(coarse_mesh)))

P2_coarse = FunctionSpace(coarse_mesh, "CG", 2)
P1_fine = FunctionSpace(fine_mesh, "CG", 1)

f = interpolate(Expression("sin(pi*x[0])*sin(pi*x[1])"), P2_coarse)
g = interpolate(f, P1_fine)

plot(f, title="Bad plot")
plot(g, title="Good plot")

interactive()

请注意如何在更精细的网格上看到粗略 P2 三角形的轮廓。

我一直在做一些自适应改进来完成这项工作（见下面的代码）。误差指示器与总网格尺寸和网格函数总变化的比例并不完美，但您可以根据需要进行调整。下面的图片用于测试用例 #4。单元格的数量从 200 个增加到大约 24,000 个，这可能有点超过顶部，但结果相当不错。网格显示只有相关部分已被细化。您仍然可以看到的人工制品是三阶元素本身无法足够准确地表示的东西。

from dolfin import *
from numpy import abs


def compute_error(expr, mesh):
    DG = FunctionSpace(mesh, "DG", 0)
    e = project(expr, DG)
    err = abs(e.vector().array())
    dofmap = DG.dofmap()
    return err, dofmap


def refine_by_bool_array(mesh, to_mark, dofmap):
    cell_markers = CellFunction("bool", mesh)
    cell_markers.set_all(False)
    n = 0
    for cell in cells(mesh):
        index = dofmap.cell_dofs(cell.index())[0]
        if to_mark[index]:
            cell_markers[cell] = True
            n += 1
    mesh = refine(mesh, cell_markers)
    return mesh, n


def adapt_mesh(f, mesh, max_err=0.001, exp=0):
    V = FunctionSpace(mesh, "CG", 1)
    while True:
        fi = interpolate(f, V)
        v = CellVolume(mesh)
        expr = v**exp * abs(f-fi)
        err, dofmap = compute_error(expr, mesh)

        to_mark = (err>max_err)
        mesh, n = refine_by_bool_array(mesh, to_mark, dofmap)
        if not n:
            break

        V = FunctionSpace(mesh, "CG", 1)
    return fi, mesh


def show_testcase(i, p, N, fac, title1="", title2=""):
    funcs = ["sin(60*(x[0]-0.5)*(x[1]-0.5))",
             "sin(10*(x[0]-0.5)*(x[1]-0.5))",
             "sin(10*(x[0]-0.5))*sin(pow(3*(x[1]-0.05),2))"]

    mesh = UnitSquareMesh(N, N)
    U = FunctionSpace(mesh, "CG", p)
    f = interpolate(Expression(funcs[i]), U)

    v0 = (1.0/N) ** 2;
    exp = 1
    #exp = 0
    fac2 = (v0/100)**exp
    max_err = fac * fac2
    #print v0, fac, exp, fac2, max_err
    g, mesh2 = adapt_mesh(f, mesh, max_err=max_err, exp=exp)

    plot(mesh, title=title1 + " (mesh)")
    plot(f, title=title1)
    plot(mesh2, title=title2 + " (mesh)")
    plot(g, title=title2)
    interactive()


if __name__ == "__main__":
    N = 10
    fac = 0.01
    show_testcase(0, 1, 10, fac, "degree 1 - orig", "degree 1 - refined (no change)")
    show_testcase(0, 2, 10, fac, "degree 2 - orig", "degree 2 - refined")
    show_testcase(0, 3, 10, fac, "degree 3 - orig", "degree 3 - refined")
    show_testcase(0, 3, 10, 0.2*fac, "degree 3 - orig", "degree 3 - more refined")
    show_testcase(1, 2, 10, fac, "smooth: degree 2 - orig", "smooth: degree 2 - refined")
    show_testcase(1, 3, 10, fac, "smooth: degree 3 - orig", "smooth: degree 3 - refined")
    show_testcase(2, 2, 10, fac, "bumps: degree 2 - orig", "bumps: degree 2 - refined")
    show_testcase(2, 3, 10, fac, "bumps: degree 3 - orig", "bumps: degree 3 - refined")