% wangj25
clear;clc;
%% 初始数据
z=[0 48.1
8 46.97
16 44.63
24 39.98
32 38.32
40 37.69
48 37.11
56 35.98
64 35.66
72 33.09
80 32.11
88 31.96
96 31.89
120 31.34
144 31.86
168 32.51
192 31.66 ];
%% main
T=z(:,1);
S=z(:,2);
figure(1);plot(T,S);
h=1;
T0=0;TT=192;
T1=T0:h:TT;
S1=spline(T,S,T1);
z1=[T1;S1];
figure(2);plot(T1,S1);
dsdt=[];
for i=1:TT-1
    dsdt(i)=(S1(i+2)-S1(i))/(T1(i+2)-T1(i));
end
t=T1(2:TT);
figure(3);plot(t,dsdt);