Chebyshev-Jackson approximation

For our filter operators we employ the Chebyshev-Jackson approximations, used previously for electronic structure calculations [39], to the step function in (6.7). The step function... 

The Chebyshev-Jackson approximation smooths the ripples that occur in a standard Chebyshev approximation for any function with sharp features. This effect is obtained by damping the high order coefficients, c,, in the sum (6.8) by the damping factors, gf e [0,1], given by (6.10). 

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See also in sourсe #XX -- [ ]

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