Plotting a vertical line using xline with a value

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rezheen
rezheen 2025-6-10
编辑： Adam Danz 2025-6-10
Ran in:
Hello, I'm trying to plot a vertical dashed line with a value (set as a variable) I have found with my code, but it won't plot.
When I change the variable in xline to the actual number (5.5), it plots the dashed line. This is the code and the problem is very last line but it depends on previous lines. Thanks.
clear, clc
syms t k C1 C
d2s=-k; dsdt=88; t1=0; s1=0;
d2=int(d2s,t); % Find the antiderivative of acceleration wrt. t.
d2_t1=subs(d2,t1);
eqn1=dsdt==d2_t1+C1; C1=solve(eqn1,C1); % Solve for C1
dsdt=d2+C1; % Velocity function
s_=int(dsdt); s=expand(s_);
s_t1=subs(s,t1);
eqn1=s1==s_t1+C; C=solve(eqn1,C); % Solve for C
s=s+C; % Position function
% % Solve the dsdt eqn above (set = 0) for t.
dsdt1=0; eqn=dsdt1==dsdt; t_val=solve(eqn,t);
% % Solve for k with s = 242 and t=t_val
s2=242; eqn1=s2==s;
eqn=subs(eqn1, t, t_val);
k_val=solve(eqn,k);
new_s=subs(s,k,k_val); new_v=subs(dsdt,k,k_val);
new_t_val=subs(t_val,k,k_val);
v2=subs(new_v,t,new_t_val);
f=fplot(new_s); set(f,'color','b','Linewidth', 1.2);hold on;grid on;
g=fplot(new_v); set(g,'color','r','LineStyle', '--');hold on;
j=xline(0); set(j,'color','black','Linewidth', 1.5);
k=yline(0); set(k,'color','black','Linewidth', 1.5);
plot(t1,s1,'.', 'color', 'b','markersize',15);hold on;
plot(new_t_val,s2,'.', 'color', 'b','markersize',15);hold on;
plot(new_t_val,v2,'.', 'color', 'r','markersize',15);hold on;
l=xline(new_t_val); set(l,'color','r','LineStyle', '--');
Error using xline (line 35)
Value must be one of the following: 'numeric' | 'datetime' | 'categorical' | 'duration'

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采纳的回答

Adam Danz
Adam Danz 2025-6-10
编辑：Adam Danz 2025-6-10
new_t_val is symbolic. As the error message indicates, xline expects to recieve numeric, datetime, categorical, or duration values.
Convert the symbolic value to double.
l=xline(double(new_t_val));

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