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vech
unvech creates a symmetric matrix from the given vector by copying the lower triangular part to be the upper triangular part as well.
unvech
unvech(d, a)
a symmetric matrix of size \((dxd)\).
number of rows the square matrix to be formed.
a size \((d(d+1)/2x1)\) vector to be unvectorized into a symmetric \((dxd)\) matrix.