几种代价函数

SAD（Sum of Absolute Difference）=SAE（Sum of Absolute Error)即绝对误差和 
SATD（Sum of Absolute Transformed Difference）即hadamard变换后再绝对值求和 
SSD（Sum of Squared Difference）=SSE（Sum of Squared Error)即差值的平方和 
MAD（Mean Absolute Difference）=MAE（Mean Absolute Error)即平均绝对差值 
MSD（Mean Squared Difference）=MSE（Mean Squared Error）即平均平方误差

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