求教MATLAB高手<br />

修改一个程序，说的它形成完整的三对角矩阵，A=diag（a，-1）+diag（b，0）+diag（c，1），并使用反斜线运算符计算斜率。
程序如下：
function v= splinetx(x,y,u)
%SPLINETX Textbook spline function.
% v = splinetx(x,y,u) finds the piecewise cubic interpolatory
% spline S(x), with S(x(j)) = y(j), and returns v(k) = S(u(k)).
%
% See SPLINE, PCHIPTX.

% First derivatives

  h = diff(x);
  delta = diff(y)./h;
  d = splineslopes(h,delta);

% Piecewise polynomial coefficients

  n = length(x);
  c = (3delta - 2d(1:n-1) - d(2:n))./h;
  b = (d(1:n-1) - 2delta + d(2:n))./h.^2;

% Find subinterval indices k so that x(k) <= u < x(k+1)

  k = ones(size(u));
  for j = 2:n-1
  k(x(j) <= u) = j;
  end

% Evaluate spline

  s = u - x(k);
  v = y(k) + s.(d(k) + s.(c(k) + s.b(k)));


% -------------------------------------------------------

function d = splineslopes(h,delta)
% SPLINESLOPES Slopes for cubic spline interpolation.
% splineslopes(h,delta) computes d(k) = S'(x(k)).
% Uses not-a-knot end conditions.

% Diagonals of tridiagonal system

  n = length(h)+1;
  a = zeros(size(h)); b = a; c = a; r = a;
  a(1:n-2) = h(2:n-1);
  a(n-1) = h(n-2)+h(n-1);
  b(1) = h(2);
  b(2:n-1) = 2(h(2:n-1)+h(1:n-2));
  b(n) = h(n-2);
  c(1) = h(1)+h(2);
  c(2:n-1) = h(1:n-2);

% Right-hand side

  r(1) = ((h(1)+2c(1))h(2)delta(1)+ ...
  h(1)^2delta(2))/c(1);
  r(2:n-1) = 3(h(2:n-1).delta(1:n-2)+ ...
  h(1:n-2).delta(2:n-1));
  r(n) = (h(n-1)^2delta(n-2)+ ...
  (2a(n-1)+h(n-1))h(n-2)delta(n-1))/a(n-1);

% Solve tridiagonal linear system

  d = tridisolve(a,b,c,r);