请问为什么这个运行出来（图二）和函数表达式（图一）不一样呀

clc;clearT15=173;%1-5区间温度T6=198 ;%6区间温度T7=230;%7区间温度T89=257 ;%8-9区间温度T1011=25;%10-11区间温度dt=0.5;v=78/60;%传送带速度t=0:dt:435.5/v;%求解区间y=ceil(heaviside(vt)-heaviside(vt-25)).((T15-25)exp(0.251(vt-25))+25)+floor(heaviside(vt-25)-heaviside(vt-197.5)).T15+ceil(heaviside(vt-197.5)-heaviside(vt-202.5)).(((T6-T15)/5)(vt-197.5)+T15)+floor(heaviside(vt-202.5)-heaviside(vt-233).T6+ceil(heaviside(vt-233)-heaviside(vt-238)).(((T7-T6)/5)(vt-233)+T6)+floor(heaviside(vt-238)-heaviside(vt-268.5)).T7+ceil(heaviside(vt-268.5)-heaviside(vt-273.5)).(((T89-T7)/5)(vt-268.5)+T7)+floor(heaviside(vt-273.5)-heaviside(vt-339.5)).T89+ceil(heaviside(vt-339.5)-heaviside(vt-380)).(((25-T89)/96)(vt-339.5)+T89)+floor(heaviside(vt-380)).(((((25-T89)/96)(380-339.5)+T89)-25)exp(-0.00991(vt-380)))+25);plot(t,y)