function [matrix, matrixInfo] = pam20
%PAM20 substitution matrix in 1/2 bit units,
%   Expected score = -6.18, Entropy = 2.95 bits
%   Lowest score = -19, Highest score = 13
%
%   Order:
%   A  R  N  D  C  Q  E  G  H  I  L  K  M  F  P  S  T  W  Y  V  B  Z  X  *
%
%   [MATRIX,MATRIXINFO] = PAM20 returns a structure of information about
%   the matrix with fields Name, Scale, Entropy, ExpectedScore, LowestScore,
%   HighestScore and Order.

% Source:  ftp://ftp.ncbi.nih.gov/blast/matrices/
%   $Revision: 1.5 $ 

matrix = [...
    6  -8  -5  -4  -8  -5  -3  -3  -8  -6  -7  -8  -6  -9  -2  -1  -1 -16  -9  -3  -5  -4  -4 -19;...
   -8   9  -7 -12  -9  -2 -11 -11  -3  -6 -10  -1  -5 -10  -5  -4  -8  -3 -11  -9  -9  -5  -7 -19;...
   -5  -7   8   1 -13  -5  -3  -4  -1  -6  -8  -2 -11 -10  -7  -1  -3  -9  -5  -9   6  -4  -4 -19;...
   -4 -12   1   8 -16  -4   2  -4  -5  -9 -15  -6 -13 -17  -9  -5  -6 -17 -13  -9   6   0  -7 -19;...
   -8  -9 -13 -16  10 -16 -16 -11  -8  -7 -17 -16 -16 -15  -9  -4  -9 -18  -5  -7 -14 -16 -11 -19;...
   -5  -2  -5  -4 -16   9   0  -8   0  -9  -6  -4  -5 -15  -4  -6  -7 -15 -14  -8  -4   7  -6 -19;...
   -3 -11  -3   2 -16   0   8  -5  -6  -6 -10  -5  -8 -16  -7  -5  -7 -19  -9  -8   0   6  -6 -19;...
   -3 -11  -4  -4 -11  -8  -5   7 -10 -13 -12  -8 -10 -10  -7  -3  -7 -17 -16  -7  -4  -6  -6 -19;...
   -8  -3  -1  -5  -8   0  -6 -10   9 -11  -7  -8 -13  -7  -5  -7  -8  -8  -4  -7  -2  -2  -6 -19;...
   -6  -6  -6  -9  -7  -9  -6 -13 -11   9  -2  -7  -2  -3 -10  -8  -3 -16  -7   1  -7  -7  -6 -19;...
   -7 -10  -8 -15 -17  -6 -10 -12  -7  -2   7  -9   0  -4  -8  -9  -8  -7  -8  -3 -10  -8  -7 -19;...
   -8  -1  -2  -6 -16  -4  -5  -8  -8  -7  -9   7  -3 -16  -8  -5  -4 -14 -10 -10  -3  -5  -6 -19;...
   -6  -5 -11 -13 -16  -5  -8 -10 -13  -2   0  -3  11  -5  -9  -6  -5 -15 -13  -2 -12  -6  -6 -19;...
   -9 -10 -10 -17 -15 -15 -16 -10  -7  -3  -4 -16  -5   9 -11  -7 -10  -6   1  -9 -12 -16  -9 -19;...
   -2  -5  -7  -9  -9  -4  -7  -7  -5 -10  -8  -8  -9 -11   8  -3  -5 -16 -16  -7  -8  -5  -6 -19;...
   -1  -4  -1  -5  -4  -6  -5  -3  -7  -8  -9  -5  -6  -7  -3   7   0  -6  -8  -8  -2  -6  -4 -19;...
   -1  -8  -3  -6  -9  -7  -7  -7  -8  -3  -8  -4  -5 -10  -5   0   7 -15  -7  -4  -4  -7  -5 -19;...
  -16  -3  -9 -17 -18 -15 -19 -17  -8 -16  -7 -14 -15  -6 -16  -6 -15  13  -6 -18 -11 -17 -13 -19;...
   -9 -11  -5 -13  -5 -14  -9 -16  -4  -7  -8 -10 -13   1 -16  -8  -7  -6  10  -8  -7 -11  -9 -19;...
   -3  -9  -9  -9  -7  -8  -8  -7  -7   1  -3 -10  -2  -9  -7  -8  -4 -18  -8   7  -9  -8  -6 -19;...
   -5  -9   6   6 -14  -4   0  -4  -2  -7 -10  -3 -12 -12  -8  -2  -4 -11  -7  -9   6  -1  -6 -19;...
   -4  -5  -4   0 -16   7   6  -6  -2  -7  -8  -5  -6 -16  -5  -6  -7 -17 -11  -8  -1   6  -6 -19;...
   -4  -7  -4  -7 -11  -6  -6  -6  -6  -6  -7  -6  -6  -9  -6  -4  -5 -13  -9  -6  -6  -6  -6 -19;...
  -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19 -19   1;...
    ];

if nargout >1
    matrixInfo.Name = 'PAM20';
    matrixInfo.Scale = 1/2;
    matrixInfo.Entropy = 2.95 ;
    matrixInfo.ExpectedScore = -6.18;
    matrixInfo.LowestScore = -19;
    matrixInfo.HighestScore = 13;
    matrixInfo.Order = 'ARNDCQEGHILKMFPSTWYVBZX*';
end