Create an upper triangular matrix from a vector
stm_triu_from_vector.Rdstm_triu_from_vector() generates an upper triangular matrix from
a given vector. The function calls another matrix function to generate
the matrix.
stm_triu_from_vector.Rdstm_triu_from_vector() generates an upper triangular matrix from
a given vector. The function calls another matrix function to generate
the matrix.