unvec forms a square matrix from a vector of stacked columns, stacked by vec.
unvec
vec
unvec(d, a)
d
the number of rows in the square matrix to be formed.
a
a size (d^2x1) vector to be unvectorized into a (dxd) matrix.
(d^2x1)
(dxd)
a matrix of size (dxd).