simpson.m

matlab中运用Simpson求积时的求积函数

function [I step]= Simpson(f,a,b,eps) 
if(nargin==3)
    eps=1.0e-4;
end
n=2;
h=(b-a)/2;
I1=2;
I2=(subs(sym(f),findsym(sym(f)),a)+subs(sym(f),findsym(sym(f)),b))/h;
while abs(I2-I1)>eps
    n=n+1;
   h=(b-a)/n;
    I1=I2;
    I2=0;
    for i=0:n-1
      x=a+h*i;
      x1=x+h;
      I2=I2+(h/6)*(subs(sym(f),findsym(sym(f)),x)+...
               4*subs(sym(f),findsym(sym(f)),(x+x1)/2)+...
                subs(sym(f),findsym(sym(f)),x1));   
    end
    I=I2;
step=n;
end