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Dynamic modell<strong>in</strong>g <strong>of</strong> large-dimensional covariance matrices 305<br />

GE.MO<br />

GE.AA<br />

EK<br />

0.035<br />

0.035<br />

0.035<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

0.025<br />

0.025<br />

0.025<br />

0.015<br />

0.015<br />

0.015<br />

0.005<br />

0.005<br />

0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

GE.CAT<br />

0.035<br />

GE.AA<br />

0.035<br />

GE.AXP<br />

0.035<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

0.025<br />

0.025<br />

0.025<br />

0.015<br />

0.015<br />

0.015<br />

Fig. 1 Comparison <strong>of</strong> the sample covariance based (Sample) and Riskmetrics TM (RM) forecast<br />

aga<strong>in</strong>st the realized covariance (True).<br />

the Cholesky series, and then reconstruct the matrix. This leads to the forecast<strong>in</strong>g<br />

formula <strong>in</strong> Eq. (25), which def<strong>in</strong>es the drc − Chol and dsrc − Chol forecast<strong>in</strong>g<br />

models for the simple realized and shrunk realized covariance case, respectively.<br />

A drawback <strong>of</strong> this approach is that the Cholesky series do not have an <strong>in</strong>tuitive<br />

<strong>in</strong>terpretation. They are simply used as a tool to constra<strong>in</strong> the forecasts to satisfy the<br />

complicated restrictions implied by the positive def<strong>in</strong>iteness requirement. Another<br />

drawback is that the Cholesky decomposition <strong>in</strong>volves nonl<strong>in</strong>ear transformations<br />

<strong>of</strong> the orig<strong>in</strong>al series. Thus, if one can adequately forecast the nonl<strong>in</strong>ear transformation,<br />

this does not immediately mean that apply<strong>in</strong>g the <strong>in</strong>verse transformation<br />

0.005<br />

0.005<br />

0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

−0.005<br />

GE<br />

0.035<br />

GE.EK<br />

0.035<br />

EK<br />

0.035<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

True<br />

Sample<br />

RM<br />

0.025<br />

0.025<br />

0.025<br />

0.015<br />

0.015<br />

0.015<br />

0.005<br />

0.005<br />

0.005<br />

100 120 140 160 180 200 220 240 260 280<br />

100 120 140 160 180 200 220 240 260 280<br />

100 120 140 160 180 200 220 240 260 280

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