Added the following conveninence functions:

/IsSquare() check for equal dimensions of the matrix and returns a boolean
func (m *Dense) IsSquare() bool

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

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

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