symext

 symext.m

 Symmetrically extends the input vector
 Usage : xe = symext(x, ln, rn, par, sym)
 x - vector to be extended, 1xN
 ln - number of values to tack onto the left of x
 rn - number of values to tack onto the right of x
 par - parity of the extension, 
       'ee' or 'e' - repeating ext., 
       'oo' or 'o' non-repeating,
       'eo' - (2,1) extension (even on right, odd on left)
       'oe' - (1,2) extension (odd on right, even on left)
       
 sym - if par = 'e', sym gives whether we have a symmetric extension
 (sym='s') or asymmetric (sym='a')

 Written by : Justin Romberg
 Created : 9/4/2001

0001 % symext.m
0002 %
0003 % Symmetrically extends the input vector
0004 % Usage : xe = symext(x, ln, rn, par, sym)
0005 % x - vector to be extended, 1xN
0006 % ln - number of values to tack onto the left of x
0007 % rn - number of values to tack onto the right of x
0008 % par - parity of the extension,
0009 %       'ee' or 'e' - repeating ext.,
0010 %       'oo' or 'o' non-repeating,
0011 %       'eo' - (2,1) extension (even on right, odd on left)
0012 %       'oe' - (1,2) extension (odd on right, even on left)
0013 %
0014 % sym - if par = 'e', sym gives whether we have a symmetric extension
0015 % (sym='s') or asymmetric (sym='a')
0016 %
0017 % Written by : Justin Romberg
0018 % Created : 9/4/2001
0019 
0020 function xe = symext(x, ln, rn, par, sym)
0021 
0022 if (nargin < 5)
0023   sym = 's';
0024 end
0025 
0026 N = length(x);
0027 t = [fliplr(1-(1:ln)) 1:N N+1:N+rn];
0028 if ((par == 'o') | (par == 'oo'))
0029   yl = 1;
0030   yh = N;
0031 elseif ((par == 'e') | (par == 'ee'))
0032   yl = 0.5;
0033   yh = N+0.5;
0034 elseif (par == 'eo')
0035   yl = 0.5;
0036   yh = N;
0037 elseif (par == 'oe')
0038   yl = 1;
0039   yh = N+0.5;
0040 end
0041 
0042 if (abs(yl-yh)<1)
0043   tr = ones(1,ln+rn+1);
0044 else
0045   tr = zeros(size(t));
0046   p = mod(floor((t-yl)/(yh-yl)),2);
0047   i0 = find(p == 0);
0048   tr(i0) = mod(t(i0)-yl, yh-yl) + yl;
0049   i1 = find(p == 1);
0050   tr(i1) = yh - mod(t(i1)-yl, yh-yl);
0051 end
0052 
0053 tr = round(tr);
0054 if (sym == 'a')
0055   xe = (1-2*p).*x(tr);
0056 elseif (sym == 's')
0057   xe = x(tr);
0058 end