middlepad.m

来自「Matlab时频分析工具箱,希望能对大家有所帮助啊」· M 代码 · 共 178 行

function f=middlepad(f,L,dim,centering)
%MIDDLEPAD  Symmetrically zero-extends or cuts a function.
%   Usage:  h=middlepad(f,L);
%           h=middlepad(f,L,dim);
%           h=middlepad(f,L,dim,cent);
%
%   MIDDLEPAD(f,L) cuts or zero-extends f to length L by inserting
%   zeros in the middle of the vector, or by cutting in the middle
%   of the vector.
%
%   If f is whole-point even, MIDDLEPAD(f,L) will also be whole-point even.
%
%   MIDDLEPAD(f,L,dim) does the same along dimension dim.
%   
%   If f has even length, then f will not be purely zero-extended, but
%   the last element will be repeated once and multiplied by 1/2!
%   That is, the support of f will increase by one!
%
%   MIDDLEPAD(f,L,dim,cent) will cut or extend whole point even functions
%   if cent=0 (this is the default) or half point even functions if
%   cent=0.5
%
%   SEE ALSO:  ISEVEN, FIR2IIR, FFTRESAMPLE

% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

error(nargchk(2,4,nargin));

if nargin==2
  dim=[];
end;

if nargin<=3
  centering=0;
end;

if  (numel(L)~=1 || ~isnumeric(L))
  error('L must be a scalar');
end;

if rem(L,1)~=0
    error('L must be an integer.');
end;

if L<1
  error('L must be larger than 0.');
end;

[f,L,Ls,W,dim,permutedsize,order]=assert_sigreshape_pre(f,L,dim,'MIDDLEPAD');

Lorig=Ls;

% Skip the main section if there is nothing to do. This is necessary
% because some of the code below cannot handle the case of 'nothing to do'
if L~=Ls
    switch centering
      case 0

        % ---------------   WPE case --------------------------------------

        if Lorig==1
          % Rather trivial case
          f=[f(1,:);zeros(L-1,W)];

        else
          if Lorig>L
        % Cut

        if mod(L,2)==0

          % L even. Use average of endpoints.
          f=[f(1:L/2,:);(f(L/2+1,:)+f(Lorig-L/2+1,:))/2;f(Lorig-L/2+2:Lorig,:)];

        else

          % No problem, just cut.
          f=[f(1:(L+1)/2,:);f(Lorig-(L-1)/2+1:Lorig,:)];

        end;     

          else

        d=L-Lorig;

        % Extend
        if mod(Lorig,2)==0

          % Lorig even. We must split a value.

          f=[f(1:Lorig/2,:);...
             f(Lorig/2+1,:)/2;...
             zeros(d-1,W);...
             f(Lorig/2+1,:)/2;...
             f(Lorig/2+2:Lorig,:)];

        else
          % Lorig is odd, we can just insert zeros.
          f=[f(1:(Lorig+1)/2,:);zeros(d,W);f((Lorig+3)/2:Lorig,:)];

        end;

          end;
        end;

      case .5

        % ------------------ HPE case ------------------------------------

        if Lorig==1

        else
          if Lorig>L

        d=Lorig-L;
        % Cut

        if mod(L,2)==0
          % L even

          % No problem, just cut.
          f=[f(1:L/2,:);...
             f(Lorig-L/2+1:Lorig,:);];

        else

          % Average of endpoints.
          f=[f(1:(L-1)/2,:);(f((L+1)/2,:)+f(Lorig-(L-1)/2,:))/2;...
             f(Lorig-(L-1)/2+1:Lorig,:);];

        end;

          else

        d=L-Lorig;

        % Extend
        if mod(Lorig,2)==0

          % Lorig even. We can just insert zeros in the middle.

          f=[f(1:Lorig/2,:);...
             zeros(d,W);...
             f(Lorig/2+1:Lorig,:)];

        else
          % Lorig odd. We need to split a value in two
          f=[f(1:(Lorig-1)/2,:);...
             f((Lorig+1)/2,:)/2;...
             zeros(d-1,W);...
             f((Lorig+1)/2,:)/2;...
             f((Lorig-1)/2+2:Lorig,:)];

        end;

          end;

        end;

      otherwise
        error('Unsupported centering.');
    end;

end;


f=assert_sigreshape_post(f,dim,permutedsize,order);