function u=c_n(h0,r0,t0)
m=1/h0;
k0=r0*h0^2;
n=floor(t0/k0);
u=1:1:m-1;
d=1:1:m-1;
bn=(1-r0)*eye(m-1);
for k=1:m-2
    bn(k,k+1)=r0/2;
    bn(k+1,k)=r0/2;
end
a=(1+r0)*eye(m-1);
for k=1:m-2
    a(k,k+1)=-r0/2;
    a(k+1,k)=-r0/2;
end
for i=1:m-1
    u(i)=sin(pi*i*h0);
end
u=u';
for i=1:n
    d=bn*u;
    u=slove_31(a,d);
end
u