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tr_p2x

PURPOSE ^

Transform P-matrix to X-vector

SYNOPSIS ^

[X,r] = tr_p2x(P,trans)

DESCRIPTION ^

  TR_P2X  Transform P-matrix to X-vector
 
  Transforms a transition matrix P to a vector X containing
    all elements in P except the diagonal of P.
 
  CALL: [X,r] = tr_p2x(P,trans)
 
  X     = Vector of length n=r*(r-1).    [nx1]
  r     = size of P-matrix.
 
  P     = transition matrix.             [rxr]
  trans = 0: No transformation. (default)
          1: log-odds-transformation.
               y = log(x/(1-x))
 
  See also trX2P.

CROSS-REFERENCE INFORMATION ^

This function calls: This function is called by:

SUBFUNCTIONS ^

SOURCE CODE ^

001 function [X,r] = tr_p2x(P,trans)
002 % TR_P2X  Transform P-matrix to X-vector
003 %
004 % Transforms a transition matrix P to a vector X containing
005 %   all elements in P except the diagonal of P.
006 %
007 % CALL: [X,r] = tr_p2x(P,trans)
008 %
009 % X     = Vector of length n=r*(r-1).    [nx1]
010 % r     = size of P-matrix.
011 %
012 % P     = transition matrix.             [rxr]
013 % trans = 0: No transformation. (default)
014 %         1: log-odds-transformation.
015 %              y = log(x/(1-x))
016 %
017 % See also trX2P.
018 
019 
020 if nargin<2, trans=[]; end
021 if isempty(trans), trans=0; end
022 
023 r = length(P);
024 E= eye(r);
025 EE = E(:);
026 IE = find(EE==0);
027 PP = P';
028 X = PP(:);
029 X = X(IE);
030 
031 switch trans
032 
033 case 0  % No transformation
034 
035 case 1  % log-odds-transformation
036 
037   X = logOdds(X);
038 
039 otherwise
040 
041   error(['Transformation ' num2str(trans) ' not defined.']);
042 
043 end % switch
044 
045 %
046 % log-odds
047 %
048 
049 function y = logOdds(x)
050 
051 y=log(x./(1-x));
052 
053

Mathematical Statistics
Centre for Mathematical Sciences
Lund University with Lund Institute of Technology

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