exponentiated time trend
[xmat]=trend(p,nobs)
p = exponent of the time-trend
nobs = size of the matrix
xmat = (nobsx1) vector containing trend
ext=trend(2,10) // returns //! 1. ! //! 4. ! //! 9. ! //! 16. ! //! 25. ! //! 36. ! //! 49. ! //! 64. ! //! 81. ! //! 100. !