<PRE class=m name="code">% 分段線性Lagrange插值   
% 命令格式：y=lagrange1(x0,y0,x)   
% x0為節點向量，y0為對應的函數值向量，   
% x為插值點向量，返回值y為x處的函數近似值向量。   
function y=lagrange1(x0,y0,x)   
[n1,n]=size(x0);[n1,m]=size(x);   
for i=1:m   
   u=x(i);   
   if u<=x0(2)   
      y(i)=y0(1)*(u-x0(2))/(x0(1)-x0(2))+...   
         y0(2)*(u-x0(1))/(x0(2)-x0(1));   
   elseif u>=x0(n-1)   
      y(i)=y0(n-1)*(u-x0(n))/(x0(n-1)-x0(n))+...   
         y0(n)*(u-x0(n-1))/(x0(n)-x0(n-1));   
   else   
      for k=2:n-1   
         if u>=x0(k) & u<=x0(k+1)   
            y(i)=y0(k)*(u-x0(k+1))/(x0(k)-x0(k+1))+...   
               y0(k+1)*(u-x0(k))/(x0(k+1)-x0(k));   
         end   
      end   
   end   
end    
y;   
   
   
</PRE>  
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