非常好用的MATLAB程序

				%x=-1:0.01:1;
				%y1=5000./(1+25.*x.^2).^3.*x.^2-50./(1+25.*x.^2).^2;
				function sm=sanci2(x,y,x1)
				y1=0;
				y11=0;
				n=length(x);
				h(1)=x(2)-x(1);
				for i=2:n-1
				    h(i)=x(i+1)-x(i);
				    lm(i)=h(i)/(h(i-1)+h(i));
				    mu(i)=1-lm(i);
				    c1(i)=3*(lm(i)*(y(i)-y(i-1))/h(i-1)+mu(i)*(y(i+1)-y(i))/h(i));
				end
				c1(1)=3*(y(2)-y(1))/h(1)-h(1)*y1/2;
				c1(n)=3*(y(n)-y(n-1))/h(n-1)-h(n-1)*y11/2;
				c(1:n)=c1(1:n);
				a=2*ones(1,n);
				b=[lm(2:n-1) 1];
				d=[1 mu(2:n-1)];
				X=trisys(d,a,b,c);
				m(1:n)=X;
				%x1=-0.9:0.1:0.9;
				L=length(x1);
				for k=1:L
				    for i=1:n-1
				        if (x1(k)>=x(i)&x1(k)				            t=(x1(k)-x(i))/h(i);
				            u1=(1+2*t)*(t-1)^2;
				            u2=t*(t-1)^2;
				            u3=t^2*(3-2*t);
				            u4=t^2*(t-1);
				            sm(k)=y(i)*u1+h(i)*m(i)*u2+y(i+1)*u3+h(i)*m(i+1)*u4;
				       end
				   end
				end
				%plot(x,fg(x),x1,sm,'r');
				%hold on;