Added the following conveninence functions:

//IsSymmetric is a function that checks if the Matrix is symmetric
//Returns a boolean, esp. `false` if matrix is not square.
func IsSymmetric(m Matrix) bool

//IsSquare() checks for equal dimensions of the matrix and returns a boolean
func IsSquare(m Matrix) bool

//Diag() returns the diagonal elements of the Matrix as a float64 slice.
func Diag(m Matrix) []float64

//NewDiag returns a new diagonal matrix with the input slice as the diagonal elements.
func NewDiag(d []float64) *Dense

With the corresponding tests in:

func (s *S) TestConvenience(c *check.C)

--

Additionally, added some doc for the methods of the *Dense type:

// Stack the stacked matrix of a with b, where b is placed in the greater indexed rows.
// See the Stacker interface for full doc.
func (m *Dense) Stack(a, b Matrix) {...

--

Finally, changed the reference to the check package with the following line:
sed -i '' -e 's/"\(.*launchpad.*\)\"/\"gopkg.in\/check.v1\"/p' mat64/*