% mlab3.m 

function d=mlab3(t,x)
% MLAB3(T,X) provides the right side for the constant coefficient, linear, 
% nonhomogeneous system x'=A*x+g(t) given in Boyce & DiPrima, Sec 8.7, 
% Prob 8, pp 457. 

   global A 

   d=[x(2); -3*x(1)-t^2*x(2)+t];