campare3inter.m

来自「数值分析, 同济大学教材<<现代数值数学和计算>>数值分」· M 代码 · 共 51 行

function result=campare3inter(count_knot,count_dot) 
%count_knot 
%count_dot
clf 
knot=linspace(-2,2,count_knot+2); 
x=-2:0.01:2; 
y=exp(-x.^2); 
y0=exp(-knot.^2); 
plot(x,y,knot,y0,'ro');%, 
hold on; 
 
x_new=linspace(-2,2,count_dot); 
y_real=exp(-x_new.^2); 
%Lagrange 
y_lagrange=lagrange(knot,y0,x_new); 
plot(x_new,y_lagrange,'k'); 
hold on; 

%divide
y_line=zeros(1,length(x_new)); 
count_1=1; 
for j=1:count_dot 
    for i=1:count_knot+1 
        if((x_new(j)>=knot(i))&((x_new(j)<=knot(i+1)))) 
            %
y_line(count_1)=((y0(i)-y0(i+1))/(knot(i)-knot(i+1)))*(x_new(j)-knot(i))+y0(i); 
            count_1=count_1+1; 
            break;         end 
    end 
end 
plot(x_new,y_line,'b'); 
hold on; 

%spline
y_temp=[0 y0 0]; 
pp=csape(knot,y_temp,'second'); 
[breaks,coefs,npolys,ncoefs,dim]=unmkpp(pp); 
count=1; 
for j=1:count_dot 
    for i=1:count_knot+1 
        if((x_new(j)>=knot(i))&((x_new(j)<=knot(i+1)))) 
            y_spline(count)=polyval(coefs(i,:),x_new(j)-knot(i)); 
            count=count+1; 
            break; 
        end 
    end 
end 

plot(x_new,y_spline,'g'); 
result=[y_real' y_lagrange' y_line' y_spline']