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. use https://www.stata-press.com/data/r17/ipq
(Federal Reserve Economic Data, St. Louis Fed)

. tsset tq

Time variable: tq, 1919q1 to 2010q4
        Delta: 1 quarter

. twoway (tsline ip_ln)

. tsfilter cf c_cf = ip_ln, minperiod(6) maxperiod(32) trend(t_cf)

. twoway (tsline t_cf) (tsline c_cf)

. pergram c_cf

. tsfilter hp c_hp = ip_ln, smooth(1600) trend(t_hp)

. pergram c_hp

.  twoway (tsline t_hp) (tsline c_hp) (tsline ip_ln)

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