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John H. Cochrane
1 Preface 7
2 What is a time series? 8
3 ARMAmodels 10
3.1 White noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Basic ARMAmodels . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Lag operators and polynomials . . . . . . . . . . . . . . . . . 11
3.3.1 Manipulating ARMAs with lag operators. . . . . . . . 12
3.3.2 AR(1) to MA(∞) by recursive substitution . . . . . . . 13
3.3.3 AR(1) to MA(∞) with lag operators. . . . . . . . . . . 13
3.3.4 AR(p) to MA(∞), MA(q) to AR(∞), factoring lag
polynomials, and partial fractions . . . . . . . . . . . . 14
3.3.5 Summary of allowed lag polynomial manipulations . . 16
3.4 Multivariate ARMAmodels. . . . . . . . . . . . . . . . . . . . 17
3.5 Problems and Tricks . . . . . . . . . . . . . . . . . . . . . . . 19
4 The autocorrelation and autocovariance functions. 21
4.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2 Autocovariance and autocorrelation of ARMA processes. . . . 22
4.2.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 25
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4.3 A fundamental representation . . . . . . . . . . . . . . . . . . 26
4.4 Admissible autocorrelation functions . . . . . . . . . . . . . . 27
4.5 Multivariate auto- and cross correlations. . . . . . . . . . . . . 30
5 Prediction and Impulse-Response Functions 31
5.1 Predicting ARMAmodels . . . . . . . . . . . . . . . . . . . . 32
5.2 State space representation . . . . . . . . . . . . . . . . . . . . 34
5.2.1 ARMAs in vector AR(1) representation . . . . . . . . 35
5.2.2 Forecasts fromvector AR(1) representation. . . . . . . 35
5.2.3 VARs in vector AR(1) representation. . . . . . . . . . . 36
5.3 Impulse-response function . . . . . . . . . . . . . . . . . . . . 37
5.3.1 Facts about impulse-responses . . . . . . . . . . . . . . 38
6 Stationarity and Wold representation 40
6.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.2 Conditions for stationary ARMA