# Why I can't plot a line with my function???

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Man Ting Ching on 11 Aug 2018
Edited: Stephen Cobeldick on 12 Aug 2018
As shown below, my function can only plot dots instead of solid lines, do anyone knows why? Thank you
%Finding indoor temperature
function [dTin] = getTin_00(Tin) %Input of function should be Tin = 5 and Theater = 40 normally
dt =0.1;
m = 4.9;
Tout = 5;
Theater = 40;
M = 0.25;
c = 1005.4;
Ar = 2.8197;
Aw = 10.2042;
Uwall = 0.0069;
Uroof = 0.0179;
dQheater = (Theater-Tin)*M*c*dt;
dQloss = (Tin-Tout)*Ar*Uroof*dt+(Tin-Tout)*Aw*Uwall*dt;
dTin = (dQheater - dQloss)/(m*c);
for t = 0:0.1:200 %increment 0.1 is equal to dt
dQheater = (Theater-Tin)*M*c*dt;
dQloss = (Tin-Tout)*Ar*Uroof*dt+(Tin-Tout)*Aw*Uwall*dt;
dTin = (dQheater - dQloss)/(m*c);
Tin = Tin+dTin;
if Tin <= 21
Theater = 40;
end
if Tin >= 24
Theater = 0;
end
figure(1);
plot(t,Tin,'.r');
title('The change in temperature over 200 seconds');
xlabel('Time');
ylabel('Internal temperature');
hold on;
grid on;
axis tight;
disp(Tin)
end
end
Man Ting Ching on 11 Aug 2018
Thank you! Appreciate it :D

Ameer Hamza on 11 Aug 2018
As Stephen pointed out, you are only plotting one point at a time, therefore the can't join to form a line. One way is to assign all the values in a vector and then plot it at the end of the loop. As an alternate approach, you can use line handle object to dynamically draw as in the following example
function [dTin] = getTin_00(Tin) %Input of function should be Tin = 5 and Theater = 40 normally
dt =0.1;
m = 4.9;
Tout = 5;
Theater = 40;
M = 0.25;
c = 1005.4;
Ar = 2.8197;
Aw = 10.2042;
Uwall = 0.0069;
Uroof = 0.0179;
dQheater = (Theater-Tin)*M*c*dt;
dQloss = (Tin-Tout)*Ar*Uroof*dt+(Tin-Tout)*Aw*Uwall*dt;
dTin = (dQheater - dQloss)/(m*c);
p = plot(0,0,'r');
p.XData = [];
p.YData = [];
title('The change in temperature over 200 seconds');
xlabel('Time');
ylabel('Internal temperature');
grid on
axis tight;
for t = 0:0.1:200 %increment 0.1 is equal to dt
dQheater = (Theater-Tin)*M*c*dt;
dQloss = (Tin-Tout)*Ar*Uroof*dt+(Tin-Tout)*Aw*Uwall*dt;
dTin = (dQheater - dQloss)/(m*c);
Tin = Tin+dTin;
if Tin <= 21
Theater = 40;
end
if Tin >= 24
Theater = 0;
end
p.XData = [p.XData t];
p.YData = [p.YData Tin];
disp(Tin)
end
end
Man Ting Ching on 12 Aug 2018
Thank you again! Appreciate it :)