How do I get all functions in this code on one figure? It is only displaying the plot from the first function.

Question

Mohannad Abboushi 2016-2-5

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/266851-how-do-i-get-all-functions-in-this-code-on-one-figure-it-is-only-displaying-the-plot-from-the-first

编辑： Walter Roberson 2016-3-26

    function question1
  y=1;
  h=.02;
  t=0
  tic
  for i=1:2500
      hold on
      t(i+1)=t(i)+h;
      y(i+1)=y(i)+h*f(t(i),y(i))
      plot(t,y,'r--')
      xlabel('t'); ylabel('y')
      title('Eulers Method for function question1')
  end
function actual=g(t,y)
actual=((5*ones*exp(-(2*t)))-(3*ones*exp(-(4*t))))/2;
figure(2)
hold all
plot(t,y);
function question1=f(t,y)
question1=(3*ones*exp(-(4*t)))-2*y;
function error=h(t,error)
error=abs(actual-question1)/actual;
figure(3)
plot(t,error,':')
xlabel('t') % Labels ??x?? axis
ylabel('Error') % Labels ??y?? axis
title('Error using Euler Method');

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Mohannad Abboushi 2016-2-5

The bottom code is supposed to be included as well. Sorry I am a beginner in Matlab.

Muhammad Fahad 2016-3-26

编辑：Walter Roberson 2016-3-26

在 MATLAB Online 中打开

Actually I want to solve the system of two coupled differential equations in MATLAB by using implicit Euler's Method.My teacher suggests me to use the command "fsolve".Here I am providing the MATLAB code that I construct.I know there must be a very stupid error at line 13 but anyways help me to solve this problem: clear all clc

f = @(y) [-80.6*y(1)+119.4*y(2); 79.6*y(1)-120.4*y(2)];
h=1/100;
y(:,1)=[1 ; 4]; t(1)=0;
for i =1:2
      y(:,i+1)=fsolve(@(z) -z+y(:,i)+h*f(z),[-10 10])
      t(i+1)=t(i)+h;
  end
      plot(t,y(1,:),'b',t,y(2,:),'b')
  hold on
      ts=0:0.001:1;
      ys(1,:)=(3)*exp(-ts)+(-2)*exp(-200*ts);
      ys(2,:)=(2)*exp(-ts)+(2)*exp(-200*ts);
         plot(ts,ys(1,:),'r',ts,ys(2,:),'g')

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Answer 1

Walter Roberson 2016-2-6

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/266851-how-do-i-get-all-functions-in-this-code-on-one-figure-it-is-only-displaying-the-plot-from-the-first#answer_208775

在 MATLAB Online 中打开

When you used

h=.02;

you "overshadowed" the meaning of h as a function, so your h function will never be called.

You have no call to your "g" function.

Caution: you start your "g" function with "hold all" after the figure(2). When you have a hold all before you have plotted anything, the default axes limits of [0 1] are frozen and nothing outside of that limit will be plotted. You should not use "hold all" or "hold on" unless you are certain you have plotted something up to the maximum range already, or unless you have set the axes limits manually using xlim() / ylim() or set() of the axes XLim and YLim properties.