title: Non-Conformable Arrays when Doing Matrix Multiplication in R
body: <p>I am trying to implement Kernel Ridge Regression in R.</p>
  
  <p>The formula is:</p>
  
  <pre><code>alpha &lt;- ((lambda.I + K)^(-1)) * y
  </code></pre>
  
  <p>Lambda = 0.1. I = identity matrix the same size as K. y is a feature vector that has the same number of rows as K.</p>
  
  <p>So I tried this in R:</p>
  
  <pre><code>I &lt;- diag(nrow(df_matrix)
  lambda &lt;- 0.1
  alpha &lt;- (lambda * I + df_matrix) ^ (-1) * df_vector
  </code></pre>
  
  <p>I get the following error</p>
  
  <pre><code>Error in (0.1 * I + df_matrix)^(-1) * df_vector : non-conformable arrays
  </code></pre>
  
  <p>Here's some information on my dataset</p>
  
  <pre><code>&gt; nrow(df_matrix)
  [1] 8222
  &gt; ncol(df_matrix)
  [1] 8222
  &gt; nrow(df_vector)
  [1] 8222
  &gt; nrow(I)
  [1] 8222
  &gt; ncol(I)
  [1] 8222
  &gt; class(df_matrix)
  [1] "matrix"
  &gt; class(df_vector)
  [1] "matrix"
  </code></pre>