function X=jia1(A,t,n)
a=eig(A);A=[1 ]
Q=eye(n);
syms s
r(1)=exp(a(1)*t);
S=zeros(n,n);
S=S+r(1)*Q;
for i=2:n;
    r1=inline(r(i-1));
    r(i)=int(exp(a(i)*(t-s))*r1(s),s,0,t);
    Q=(A-a(i-1)*eye(n))*Q;
    S=S+r(i)*Q;
end
X=S;