title: Error plotting data read from csv file
body: <p>I am getting the followin error when trying to plot in GNU/octave:</p>
  
  <pre><code>octave:22&gt; plot(b(:,2),b(:,4))
  error: invalid conversion from real matrix to real scalar
  error: __calc_dimensions__: expecting graphics handle as only argument
  error: called from:
  error:   /usr/share/octave/3.6.2/m/plot/private/__go_draw_axes__.m at line 55, column 8
  error:   /usr/share/octave/3.6.2/m/plot/private/__go_draw_figure__.m at line 167, column 19
  error:   /usr/share/octave/3.6.2/m/plot/__gnuplot_drawnow__.m at line 86, column 5
  octave:23&gt; 
  </code></pre>
  
  <p>The variable <i>b</i> is loaded from a <i>csv</i> file, as follows:</p>
  
  <pre><code>b=csvread("my.csv")
  </code></pre>
  
  <p>Content of <i>my.csv</i></p>
  
  <pre><code>1,40.0942,0.775539,18.658
  2,40.1882,0.857556,415.677
  3,40.2818,0.858294,233.934
  4,40.3748,0.887273,348.503
  5,40.4669,0.908618,27.0149
  6,40.558,0.908496,234.81
  7,40.6478,0.911826,58.3943
  8,40.7362,0.922848,204.128
  9,40.823,0.928547,7.75615
  10,40.908,0.920065,0.0654867
  </code></pre>
  
  <p>Sadly,sometimes the erros happens, others do not. (octave bug?)</p>
  
  <p>Does anyone knows what is going on?</p>
  
  <p>By the way, my systems is: Ubuntu 12.11, octave 3.6.2, Linux kernel 3.5.00-22-generic</p>
  
  <p><b>Edit:</b></p>
  
  <p>I think it is a bug. The foregoing error is caused by a <i>plot</i> called after a <i>plotyy</i>. To reproduce the error, execute these commands:</p>
  
  <pre><code>1&gt; b=csvread("my.csv");
  2&gt; plot(b(:,2),b(:,4))
  3&gt; plotyy(b(:,1),b(:,2),b(:,1),b(:,4))
  4&gt; plot(b(:,2),b(:,4))
  </code></pre>