Dear all, I tried to inspect the magnetic field profile in one snap of my enzo output with the code: ############################################# from yt.mods import * # set up our namespace import numpy as np import pylab as P def _BMag(field, data): return np.sqrt(data["Bx"] * data["Bx"] + data["By"] * data["By"] + data["Bz"] * data["Bz"]) add_field("BMag", function=_BMag) c = pf.h.find_max('BMag')[1] ax = 0 ray = pf.h.ortho_ray(ax, (c[1], c[2])) P.subplot(212) P.semilogy(ray['x'], ray['BMag']) P.xlabel('x') P.ylabel('BMag') print "works" P.savefig("BMag_lineplot.png") ############################################# But keep getting this error message. ############################################# (yt-x86_64)[yd742@ria run5]$ python ytplots_BMag_lineplot_dai.py yt : [INFO ] 2016-03-12 19:19:31,279 Parameters: current_time = 0 yt : [INFO ] 2016-03-12 19:19:31,279 Parameters: domain_dimensions = [128 64 64] yt : [INFO ] 2016-03-12 19:19:31,279 Parameters: domain_left_edge = [-6000. -3000. -3000.] yt : [INFO ] 2016-03-12 19:19:31,280 Parameters: domain_right_edge = [ 6000. 3000. 3000.] yt : [INFO ] 2016-03-12 19:19:31,280 Parameters: cosmological_simulation = 0.0 Parsing Hierarchy 100% ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| Time: 00:00:00 yt : [INFO ] 2016-03-12 19:19:31,285 Gathering a field list (this may take a moment.) yt : [INFO ] 2016-03-12 19:19:31,290 Adding unknown field Phi to list of fields yt : [INFO ] 2016-03-12 19:19:31,290 Adding unknown field B_Vorticity2 to list of fields yt : [INFO ] 2016-03-12 19:19:31,290 Adding unknown field B_Vorticity3 to list of fields yt : [INFO ] 2016-03-12 19:19:31,290 Adding unknown field B_Vorticity1 to list of fields yt : [INFO ] 2016-03-12 19:19:31,290 Adding unknown field B_Div to list of fields yt : [INFO ] 2016-03-12 19:19:32,705 Max Value is 8.56382e-05 at -2501.9531250000000000 29.2968750000000000 228.5156250000000000 in grid EnzoGrid_0005 at level 3 (16, 16, 15) yt : [INFO ] 2016-03-12 19:19:32,705 Getting field x from 4 Traceback (most recent call last): File "ytplots_BMag_lineplot_dai.py", line 45, in <module> P.subplot(212) File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/site-packages/matplotlib-1.3.0-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 896, in subplot fig = gcf() File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/site-packages/matplotlib-1.3.0-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 450, in gcf return figure() File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/site-packages/matplotlib-1.3.0-py2.7-linux-x86_64.egg/matplotlib/pyplot.py", line 423, in figure **kwargs) File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/site-packages/matplotlib-1.3.0-py2.7-linux-x86_64.egg/matplotlib/backends/backend_tkagg.py", line 79, in new_figure_manager return new_figure_manager_given_figure(num, figure) File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/site-packages/matplotlib-1.3.0-py2.7-linux-x86_64.egg/matplotlib/backends/backend_tkagg.py", line 87, in new_figure_manager_given_figure window = Tk.Tk() File "/home/yd742/software/withpysci/yt-x86_64/lib/python2.7/lib-tk/Tkinter.py", line 1745, in __init__ self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use) _tkinter.TclError: no display name and no $DISPLAY environment variable ############################################# I'm using yt Version = 2.6.1 Changeset = c994959ed3be ======================= I would very much appreciate it if anyone could help me on this. Thank you so much. Regards, Dai