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x=-1:0.01:1; 
y1=-50./(1+25.*x.^2).^2.*x; 
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)*(fg(x(i))-fg(x(i-1)))/h(i-1)+mu(i)*(fg(x(i+1))-fg(x(i)))/h(i)); 
end 
c(1:n-2)=c1(2:n-1); 
m(1)=y1(1); 
m(n)=y1(n); 
c(1)=c(1)-lm(2)*m(1); 
c(n-2)=c(n-2)-mu(n-1)*m(n); 
a=2*ones(1,n-2); 
b=lm(3:n-1); 
d=mu(2:n-2); 
X=trisys(d,a,b,c); 
m(2:n-1)=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)<=x(i+1)) 
            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)=fg(x(i))*u1+h(i)*m(i)*u2+fg((i+1))*u3+h(i)*m(i+1)*u4; 
       end 
   end 
end 
plot(x,fg(x),x1,sm,'r'); 
hold on;