title: In R, after installed a package,' pixmap', Error in file(file, open = "rb") : cannot open the connection
body: <p>I'm learning R programming, using the book, "The Art of R Programming".
  In chapter 3.2.3 Extended Example: Image Manipulation. The author Matloff tries to use a Mount Rushmore gray-scale image to illustrate that the image is stored in matrix. He used a library called pixmap. And I downloaded the package, installed it.</p>
  
  <pre><code>&gt; library(pixmap)
  &gt; mtrush1 &lt;- read.pnm("mtrush1.pgm")
  &gt; mtrush1
  Pixmap image
    Type          : pixmapGrey
    Size          : 194x259
    Resolution    : 1x1
    Bounding box  : 0 0 259 194
  &gt; plot(mtrush1) 
  </code></pre>
  
  <p>This is what the book has written, and I tried to run this, but got the error message,</p>
  
  <pre><code>&gt; library(pixmap)
  &gt; mtrush1 &lt;- read.pnm("mtrush1.pgm")
  Error in file(file, open = "rb") : cannot open the connection
  In addition: Warning message:
  In file(file, open = "rb") :
    cannot open file 'mtrush1.pgm': No such file or directory
  starting httpd help server ... done
  </code></pre>
  
  <p>What does this mean? cannot open the connection? And also the mtrush1.pgm does not exist? How should I fix it here? Any help? Much appreciated.</p>