RuntimeError: Invalid DISPLAY variable
<p>I am running my python script in another machine by using <code>ssh</code> command in <code>linux</code>. I have also run this command :</p>

<pre><code>source ~/.bashrc 
</code></pre>

<p>after logging in the other machine, in order to define the proper paths in the new machine. I was getting the error message for running the following python code lines even I have tried to follow the instruction in <a href="https://stackoverflow.com/questions/21321292/using-matplotlib-when-display-is-undefined">this question</a> by defining the backend.</p>

<pre><code>&gt;&gt;&gt; import matplotlib
&gt;&gt;&gt; import pylab as plt
&gt;&gt;&gt; matplotlib.use('Agg')
&gt;&gt;&gt; import numpy as np
&gt;&gt;&gt; x=np.arange(0,2,0.001)
&gt;&gt;&gt; y=np.sin(x)**2+4*np.cos(x)
&gt;&gt;&gt; fig = plt.figure()
&gt;&gt;&gt; plt.plot(x,y,'r.')     
</code></pre>

<p>The error message</p>

<pre><code>This probably means that Tcl wasn't installed properly.
Traceback (most recent call last):
  File "Systematic_Optimised.py", line 513, in &lt;module&gt;
    fig = plt.figure()
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/pyplot.py", line 435, in figure
    **kwargs)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 47, in new_figure_manager
    return new_figure_manager_given_figure(num, thisFig)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 54, in new_figure_manager_given_figure
    canvas = FigureCanvasQTAgg(figure)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 72, in __init__
    FigureCanvasQT.__init__(self, figure)
  File "/vol/aibn84/data2/zahra/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4.py", line 68, in __init__
    _create_qApp()
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt5.py", line 138, in _create_qApp
    raise RuntimeError('Invalid DISPLAY variable')
RuntimeError: Invalid DISPLAY variable
</code></pre>

<p>any suggestion how to fix the problem</p>