ji2.m

de Boor 求值算法求作二次和三次B-样条插值曲线

function N=Ji2(i,j,u)
switch j
    case i+1  
        if (u(i+3)-u(i+1))*(u(i+3)-u(i+2))==0
            a=0;
        else
            a=(u(j+1)-u(i+1))*(u(i+3)-u(j+1))/((u(i+3)-u(i+1))*(u(i+3)-u(i+2)));
        end
        if (u(i+4)-u(i+2))*(u(i+3)-u(i+2))==0
            b=0;
        else
            b=(u(j+1)-u(i+2))*(u(i+4)-u(j+1))/((u(i+4)-u(i+2))*(u(i+3)-u(i+2)));
        end
        N=a+b;
    case i+2
        if (u(i+4)-u(i+2))*(u(i+4)-u(i+3))==0
            N=0;
        else
            N=(u(i+4)-u(j+1))^2/((u(i+4)-u(i+2))*(u(i+4)-u(i+3)));
        end
    otherwise
        N=0;
end