title: How to use corrplot with simple matrices
body: <p>I have a simple 8 by 8 matrix</p>
  
  <pre><code>M &lt;- matrix(rnorm(64), nrow=8, ncol=8) 
  </code></pre>
  
  <p>How should I transform it to plot it with <code>library(corrplot)</code>? Without transformation the error is:</p>
  
  <pre><code>corrplot.mixed(M)
  </code></pre>
  
  <blockquote>
    <p>Error in corrplot(corr, type = "upper", method = upper, diag = TRUE, tl.pos = tl.pos,  : 
          The matrix is not in [-1, 1]!
    which I guess would assume that the matrix should be [-1, 1]?</p>
  </blockquote>