upfirdn.m

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%UPFIRDN  Upsample, apply a specified FIR filter, and downsample a signal.
%   UPFIRDN(X,H,P,Q) is a cascade of three systems applied to input signal X:
%         (1) Upsampling by P (zero insertion).
%         (2) FIR filtering with the filter specified by the impulse response 
%             given in H.
%         (3) Downsampling by Q (throwing away samples).
%   UPFIRDN uses an efficient polyphase implementation.
%
%   Usually X and H are vectors, and the output is a (signal) vector. 
%   UPFIRDN permits matrix arguments under the following rules:
%   If X is a matrix and H is a vector, each column of X is filtered through H.
%   If X is a vector and H is a matrix, each column of H is used to filter X.
%   If X and H are both matrices with the same number of columns, then the i-th
%      column of H is used to filter the i-th column of X.
%
%   Specifically, these rules are carried out as follows.  Note that the length
%   of the output is Ly = ceil( ((Lx-1)*P + Lh)/Q ) where Lx = length(X) and 
%   Lh = length(H). 
%
%      Input Signal X    Input Filter H    Output Signal Y   Notes
%      -----------------------------------------------------------------
%   1) length Lx vector  length Lh vector  length Ly vector  Usual case.
%   2) Lx-by-Nx matrix   length Lh vector  Ly-by-Nx matrix   Each column of X
%                                                            is filtered by H.
%   3) length Lx vector  Lh-by-Nh matrix   Ly-by-Nh matrix   Each column of H is
%                                                            used to filter X.
%   4) Lx-by-N matrix    Lh-by-N matrix    Ly-by-N matrix    i-th column of H is
%                                                            used to filter i-th
%                                                            column of X.
%
%   UPFIRDN(X,H,P)  uses Q=1 as the default.
%   UPFIRDN(X,H)    uses P=1 and Q=1 as defaults.
%
%   For an easy-to-use alternative to UPFIRDN, which does not require you to 
%   supply a filter or compensate for the signal delay introduced by filtering,
%   use RESAMPLE.
%
%   See also RESAMPLE, INTERP, DECIMATE, FIR1, INTFILT.

%   Author(s): James McClellan, 1-29-95
%   Copyright (c) 1988-98 by The MathWorks, Inc.
%   $Revision: 1.6 $  $Date: 1997/12/02 18:36:41 $

%   C MEX-file.