function y = lin4a(x)
%
% eigenvalues of A are   +/- i and +/- i sqrt(2)
% which have absolute value 0.8
%

A = [
   1.12408879929808  -5.95885105986366  -8.21507330737195   6.88423016974016
   0.28085203159774   1.85640701052264   0.88809169222244  -1.67117810516100
   0.47485892534435  -0.37383235000468  -3.59926720334469   2.70516846342119
   0.48174885855324   2.16667900535984  -2.14874689149754   0.61877139352397
];

b = [0;0;0;0] ;

y = A*x + b;