implicit_plot3d

edit

Hi , I'm a new user of sagemath and when i evaluate :

x, y = var('x,y')
plot3d(x^2 + y^2, (x,-2,2), (y,-2,2))

there is an error the message is as below ,I tried many times but still can't solve this problem ,how can I solve this problem ? thank you very much.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "_sage_input_4.py", line 10, in <module>
    exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8 -*-\\n" + _support_.preparse_worksheet_cell(base64.b64decode("aW1wbGljaXRfcGxvdDNkKHheMit5XjIrel4yPT00LCAoeCwgLTMsIDMpLCAoeSwgLTMsMyksICh6LCAtMywzKSk="),globals())+"\\n"); execfile(os.path.abspath("___code___.py"))
  File "", line 1, in <module>
      File "/tmp/tmpR_uNrC/___code___.py", line 3, in <module>
    exec compile(u'implicit_plot3d(x**_sage_const_2 +y**_sage_const_2 +z**_sage_const_2 ==_sage_const_4 , (x, -_sage_const_3 , _sage_const_3 ), (y, -_sage_const_3 ,_sage_const_3 ), (z, -_sage_const_3 ,_sage_const_3 ))
  File "", line 1, in <module>
      File "/usr/local/sage-5.5-linux-32bit-ubuntu_12.04.1_lts-i686-Linux/local/lib/python2.7/site-packages/sage/misc/displayhook.py", line 176, in displayhook
    print_obj(sys.stdout, obj)
  File "/usr/local/sage-5.5-linux-32bit-ubuntu_12.04.1_lts-i686-Linux/local/lib/python2.7/site-packages/sage/misc/displayhook.py", line 144, in print_obj
    print >>out_stream, `obj`
  File "base.pyx", line 81, in sage.plot.plot3d.base.Graphics3d.__repr__ (sage/plot/plot3d/base.c:2939)
  File "base.pyx", line 1128, in sage.plot.plot3d.base.Graphics3d.show (sage/plot/plot3d/base.c:11464)
  File "base.pyx", line 621, in sage.plot.plot3d.base.Graphics3d.export_jmol (sage/plot/plot3d/base.c:6070)
  File "base.pyx", line 1440, in sage.plot.plot3d.base.Graphics3dGroup.jmol_repr (sage/plot/plot3d/base.c:15145)
  File "base.pyx", line 1643, in sage.plot.plot3d.base.TransformGroup.jmol_repr (sage/plot/plot3d/base.c:17385)
  File "base.pyx", line 1643, in sage.plot.plot3d.base.TransformGroup.jmol_repr (sage/plot/plot3d/base.c:17385)
  File "implicit_surface.pyx", line 1076, in sage.plot.plot3d.implicit_surface.ImplicitSurface.jmol_repr (sage/plot/plot3d/implicit_surface.c:12398)
  File "index_face_set.pyx", line 708, in sage.plot.plot3d.index_face_set.IndexFaceSet.jmol_repr (sage/plot/plot3d/index_face_set.c:8152)
  File "index_face_set.pyx", line 124, in sage.plot.plot3d.index_face_set.format_pmesh_vertex (sage/plot/plot3d/index_face_set.c:2812)
SystemError: Negative size passed to PyString_FromStringAndSize