Most of what a devops person does is in fact development but it is of the non value adding variety. Basically a devops person spends the vast majority of their time configuring common off the shelf software, scripting this or that, etc.
A singular matrix is a matrix which has no inverse because its determinant is zero. If you recall, the inverse of a matrix is. 1/ ad-bc multiplied by: [ d -b ] [-c a ] If ad-bc = 0, then the inverse matrix would not exist because 1/0 is undefined, and hence it would be a singular matrix. E.g.
The identity matrix I n of size n is the n-by-n matrix in which all the elements on the main diagonal are equal to 1 and all other elements are equal to 0, e.g. It is a square matrix of order n, and also a special kind of diagonal matrix.