title: Weird result from Inversion of matrix using Package "Matrix" with negative sign in R
body: <p>It is normal when using standard matrix function and get the inversion of negative matrix by solve()</p>
  <pre><code>B &lt;- matrix(c(2,1,1,2),nrow=2,ncol=2)
  solve(-B)
             [,1]       [,2]
  [1,] -0.6666667  0.3333333
  [2,]  0.3333333 -0.6666667
  </code></pre>
  <p>However it produce the opposite matrix when defining the matrix using &quot;Matrix&quot; Package</p>
  <pre><code>C &lt;- Matrix(c(2,1,1,2),nrow=2,ncol=2)
  solve(-C)
  2 x 2 Matrix of class &quot;dsyMatrix&quot;
             [,1]       [,2]
  [1,]  0.6666667 -0.3333333
  [2,] -0.3333333  0.6666667
  </code></pre>
  <p>now solve(-C) is the same as solve(C), Why?</p>