43. The machine-implemented method of claim 40 wherein decomposing the matrix W comprises performing a singular value decomposition of W, represented by 
 W=USV T where M is the number of instances, M is the maximum number of segments corresponding to an instance, U is the M×R left singular matrix with row vectors u i (1≦i≦M), S is the R×R diagonal matrix of singular values s 1 ≧s 2 ≧ . . . ≧s R >0, V is the N×R right singular matrix with row vectors v j (1≦j≦N), R≦min (M, N), and T denotes matrix transposition.
43. The machine-implemented method of claim 40 wherein decomposing the matrix W comprises performing a singular value decomposition of W, represented by 
 W=USV T where M is the number of instances, M is the maximum number of segments corresponding to an instance, U is the M×R left singular matrix with row vectors u i (1≦i≦M), S is the R×R diagonal matrix of singular values s 1 ≧s 2 ≧ . . . ≧s R >0, V is the N×R right singular matrix with row vectors v j (1≦j≦N), R≦min (M, N), and T denotes matrix transposition. 44. The machine-implemented method of claim 43 wherein a feature vector ū i is calculated as 
 ū i =u i S where u i is a row vector associated with an instance i, and S is the singular diagonal matrix.