clear,clc,close all;

figure('color',[1,1,1]);hold on

x = -5:0.1:5; df = [1,5,30];

for n = 1:length(df)

   y = tpdf(x,df(n));plot(x,y,'linewidth',1);

end

text(-1,0.15,'$$\leftarrow n=1$$','interpreter','latex');

text(-0.8,0.25,'$$\leftarrow n=5$$','interpreter','latex');

text(-1.8,0.35,'$$n=30\rightarrow$$','interpreter','latex');

axis([-5,5,0,0.45]);grid on

%%%%%%%%%%% 上 alpha 分位数

figure('color',[1,1,1]);hold on

x = -5:0.1:5; alpha = 0.05; n = 5;

y = tpdf(x,n);plot(x,y,'linewidth',2);

fill([tinv(1-alpha,n),5,5:-0.01:tinv(1-alpha,n),tinv(1-alpha,n),tinv(1-alpha,n)],...

   [0,0,tpdf(5,n),tpdf(5:-0.01:tinv(1-alpha,n),n),0],'m');

text(1,0.35,'$$n=5$$','interpreter','latex','fontsize',18);

text(tinv(1-alpha,n)-1,-0.02,'$$t_{\alpha}(n)=2.1050$$','interpreter',...

   'latex','color','r','fontsize',18);

text(2.43,0.03,'$$\longleftarrow$$','interpreter','latex','fontsize',18,'rotation',45);

text(2.3,0.07,'$$\alpha=0.05$$','interpreter','latex','fontsize',18);

plot(tinv(1-alpha,n),0,'ro','MarkerEdgeColor','r','MarkerFaceColor','r')