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

Question

Man Ting Ching 2018-8-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/414466-why-i-can-t-plot-a-line-with-my-function

编辑： Stephen23 2018-8-12

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 个评论
显示 -1更早的评论隐藏 -1更早的评论

Man Ting Ching 2018-8-11

Thank you! Appreciate it :D

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Ameer Hamza 2018-8-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/414466-why-i-can-t-plot-a-line-with-my-function#answer_332403

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 个评论
显示 1更早的评论隐藏 1更早的评论

Stephen23 2018-8-11

编辑：Stephen23 2018-8-12

" 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:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

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 2018-8-12