Plotting results of for loop on one graph

Hi, I am relatively unexperienced with MATLAB, so bear with me! I created a for loop where two of the values in my matrix are functions of r, and then further operations are performed with each iteration of the matrix. The values are generated but then when I try to graph them, I get either an error or no graph. Here's my code:

for r=0:0.001:1.1;

M=[-1*(r.^2)+1.3 -0.3;-0.3, -0.3*(r.^2)+0.3];

f=[1;0];

z_1=M\f;

plot(r,z_1)

end

Thank you in advance!

**As an added comment, if I try to express z_1 as z_1(r), or do this operation without the for loop, I get the error "Subscript indices must either be real positive integers or logicals" and I also don't know how to fix that...

Answer 1

[Jon]

Replace your plot(r,z_1) with this:

    plot(r,z_1,'.'); hold on

If you don't turn the "hold" to "on" then the figure is overwritten with each iteration.

You can also achieve this by adding these commands before the loop:

figure; hold on

[Kelly Berry]

Thanks Jon! I am still getting the "Subscript indices must either be real positive integers or logicals" error-any idea how to fix that?

[Jon]

When you reference a vector, you must use an integer position. For example, if you want the third element of

ex = [3 5 6 9 2];

you would type

ex(3)

if you tried

ex(.001)

You would get the error that you're seeing. You are trying to reference using non-integers, since r takes on decimal values. The example of Jae Song below shows a nice way around this problem.

[Kelly Berry]

Thank you! I finally got it!!!

[ramin esmaeilzadeh]

Realy thank you.

[faith]

can we use the same solution to plot more than one graph in each iteration of the loop? for example, I want to sketch the graph of two circles, and one line further. I, also want to shrink one of the circles in each iteration of a loop. thanks in advance

Answer 2

[Jae Song]

The z_1 matrix variable needs to have index; Please see the following code

x = 0:0.001:1.1;
s = size(x,2);  %: get the array size

for i=1:s
    r = x(i);
    M=[-1*(r.^2)+1.3 -0.3;-0.3, -0.3*(r.^2)+0.3];
    f=[1;0];
    z_1(:,i)=M\f;
end
figure(1); plot(x,z_1(1,:));
figure(2); plot(x,z_1(2,:));

[Kelly Berry]

Thanks Jae!! I used a combination of your answer and Jon's, and I finally got it to work! I definitely appreciate your help!

[Nasir Mehmood]

Hello dear Jae Song! I'm new to Matlab.

When I change

x = 0:0.001:1.1;

to

x = 0:0.01:1.1;

no plot is obtained. How to handle this issue?

Also can you describe a little about these lines:

z_1(:,i)=M\f;

and

figure(1); plot(x,z_1(1,:));

Answer 3

[Hansa Prasad]

T0=24;

m0=1;

eta=4.2;

T(1)=T0;

m(1)=m0;

C=216;

R=2;

Ta=26;

P=2;

Ts=21;

for t=1:300:1;

T(t+1)=(-1/(C*R))*(T(t)-Ta+m(t)*R*P*eta)+T(t);

plot(t,T(t))

end