matlab syms subs eval 实例

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clc;close all;clear;syms T;syms t;syms vmax;len = 150;y = vmax*(1 - exp(-t/T))y2 = vmaxy3 = vmax*exp(-t/T)%--------------------导数----------------------dy = diff(y,t)dy2 = diff(y2,t)dy3 = diff(y3,t)%-------------------衔接点---------------------yt0 = subs(dy,t,0) %dy不会改变yt2 = subs(dy3,t,2*len)%--------------------画图---------------------t = [0:0.1:len];T = 3;vmax = 5;tt = [t t+len t+2*len];yy = eval([y zeros(1,length(t))+y2 y3]);dydy = eval([dy zeros(1,length(t))+dy2 dy3]);%速度图idx = floor(length(tt)/2);cell_string{1} = '\fontsize{12}';%<15>cell_string{2} = '\uparrow';cell_string{3} = '速度';figure,plot(tt,yy) %eval求值text(tt(idx),yy(idx),cell_string,'Color','r','HorizontalAlignment','Center')%加速度图cell_string{3} = '加速度';figure,plot(tt,dydy)text(tt(idx),dydy(idx),cell_string,'Color','r','HorizontalAlignment','Center')

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