Cross-validated r-squared

A suitable criterion function for regression analysis should reflect how well the response values are predicted. In the adaptive wavelet algorithm, the criterion function considered for regression is based on the PRESS statistic and is then converted to a leave-one-out cross-validated R-squared measure as follows... 

The cross-validated R-squared criterion function is defined as... 

The most conceivable difference between the AWA when applied for regression (as opposed to classification) is the criterion function which is implemented. Here, the cross-validated R-squared criterion which is based on the PRESS statistic, is the regression criterion function which is implemented... 

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