how can i find base spline function for using cubic spline Rayleigh-Ritz method ?

in screen shot, -u(t)" -> -u(x)"

>> x=linspace(0,1,502); h=1/501;

>> global xi xim xip;

>> tic

>> for i=2:501

xi=x(i); xim=x(i-1); xip=x(i+1);

b(i)=quadl('frayritz10_8load', xim,xip);

d(i)=2/h+1/h^2*quadl('frayritz10_8stiff1',xim,xi)...

+ 1/h^2*quadl('frayritz10_8stiff2', xi, xip) ;

da(i)=-1/h+1/h^2*quadl('frayritz10_8stiff3',xi,xip);

end

>> db(3:501)=da(2:500);

>> db(2)=0;da(501)=0;

>> toc

경과 시간은 2435.024751초입니다.

>> c1=thomas(da(2:501),d(2:501),db(2:501),b(2:501));

>> c1=[0 c1 0];

>> plot(x,c1); hold on

it is my matlab code. i find only 1x501 stiffness matrix. but i want to find 𝑛×𝑛 stiffness matrix 𝐴 = [𝑎_ij] by using matlab