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

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Man Ting Ching
Man Ting Ching 2018 年 8 月 11 日
編集済み: Stephen23 2018 年 8 月 12 日
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
  1 件のコメント
Man Ting Ching
Man Ting Ching 2018 年 8 月 11 日
Thank you! Appreciate it :D

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採用された回答

Ameer Hamza
Ameer Hamza 2018 年 8 月 11 日
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
  3 件のコメント
Stephen23
Stephen23 2018 年 8 月 11 日
編集済み: Stephen23 2018 年 8 月 12 日
" One way is to assign all the values in a vector and then plot it at the end of the loop."
That is exactly what the MATLAB documentation recommends:
The code shown in this answer expands the data arrays on each loop iteration, which will be slow as MATLAB must move the data within memory on each iteration. This is a cause of many beginners writing slow code. Better practice would be to preallocate the matrix before the loop, assign the values to it inside the loop using indexing, then plot it after the loop.
Man Ting Ching
Man Ting Ching 2018 年 8 月 12 日
Thank you again! Appreciate it :)

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