title: Plot is not generating the heat map for tune model (SVM)
body: <p>I'm using R-Studio and e1071 package for SVM (Support Vector Machine). Iris dataset is the typical one used in R.</p>
  
  <p>The code is the following:</p>
  
  <pre><code>tune_model &lt;-tune(svm, Species~., data=iris,
               ranges= list(epsilon= seq(0, 1, 0.1)), #epsilon= 0, 0.1, 0.2 etc
               cost=2^(2:9)) #default cost=1
                             #if cost is too high--&gt; high penalty for non-separable points--&gt; will use too many support vectors--&gt;overfitting
                             #if cost is too low--&gt; underfitting
  plot(tune_model)
  </code></pre>
  
  <p>However I'm getting:</p>
  
  <p><a href="https://i.stack.imgur.com/10pYQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/10pYQ.png" alt="Tuning output"></a></p>
  
  <p>Whereas I should be getting a heatmap:
  <a href="https://i.stack.imgur.com/ECLqE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ECLqE.png" alt="enter image description here"></a></p>
  
  <p>What am I doing wrong?</p>