title: Can 2d convolution been represented as matrix multiplication?
body: <p>Discr. convolution can be represented as multiplication of input with matrix M.</p>
  
  <p>Where M is presented a special case of Toeplitz matrices - circulant matrices.</p>
  
  <p><strong>The questions is:</strong> is 2d convolution can also be represented as matrix multiplication?</p>
  
  <p>p.s. By dicr. convolution I mean dicr. convolution with indexing discrete samples in modulus fashion, i.e. the discrete signal is repeating 
  ....X[n-1]x[0]x[1]...x[N-1]x[0]...</p>