% solves iteratively ax+bxc=d

function x=sylvester3a(x0,a,b,c,d)
  a_1 = inv(a);
  b = a_1*b;
  d = a_1*d;
  e = 1;
  iter = 1;
  while e > 1e-8 & iter < 500
    x = d-b*x0*c;
    e = max(max(abs(x-x0)));
    x0 = x;
    iter = iter + 1;
  end
  if iter == 500
    warning('sylvester3a : Only accuracy of %10.8f is achieved after 500 iterations') 
  end