% fft1d_f:   implementation of dense FFT-based sampling operator(e.g., partial FFT, scrambled FFT etc.); 
% fft1d_t:   implementation of the transpose of dense FFT-based sampling operator;
% blk_f1d:   implementation of random block-based sensing operator (e.g., scrambled block Hadamard ensemble);
% blk_t1d:   implemenation of the transpose of the random block-based sensing operator;
% A_idwt1d:  Calculation of the equivalent sampling operator for the
% wavelet coefficients when the sensing is conducted in the spatial domain;
% At_dwt1d:  transpose operator for A_idwt1d
%