我在一个数值分析课上，我正在做一个家庭作业问题。这是Timothy Sauer的数值分析，在第二个建议活动部分。我一直在和我的教授谈论这个代码，似乎错误和近似是错误的，但我们都不能找出原因。下面的代码是我正在使用的，这是在MatLab中。有谁对欧拉·伯努利梁有足够的了解，有谁能帮上忙？

function ebbeamerror %This is for part three

   disp(['tabe of errors at x=L for each n'])
   disp(['             n ','        Aprox ','      Actual value','       Error'])
   disp(['======================================================='])
   format bank
    
   for k = 1:11
      n = 10*(2^k);
      D = sparse(1:n,1:n,6*ones(1,n),n,n);
      G = sparse(2:n,1:n-1,-4*ones(1,n-1),n,n);
      F = sparse(3:n,1:n-2,ones(1,n-2),n,n);
      S = G+D+F+G'+F';
      S(1,1) = 16;
      S(1,2) = -9;
      S(1,3) = 8/3;
      S(1,4) = -1/4;
      S(2,1) = -4;
      S(2,2) = 6;
      S(2,3) = -4;
      S(2,4) = 1;
      S(n-1,n-3)=16/17;
      S(n-1,n-2)=-60/17;
      S(n-1,n-1)=72/17;
      S(n-1,n)=-28/17;
      S(n,n-3)=-12/17;
      S(n,n-2)=96/17;
      S(n,n-1)=-156/17;
      S(n,n)=72/17;
         
      E = 1.3e10;
      w = 0.3;
      d = 0.03;
      I = w*d^3/12;
      g = -9.81;
      f = 480*d*g*w;
      h = 2/10;
      L = 2;
      x = (h^4)*f/(E*I);
      x1 = ones(n ,1);
      b = x*x1; 
      size (S);
      size(b);
      pause
      y = S\b;
      x=2;
      a = (f/(24*E*I))*(x^2)*(x^2-4*L*x+6*L^2);
      disp([n y(n) a abs(y(n)-a)])
   end 
end