How to re-run portions of code with updates variables?

Hello, for my lab assignment we have to graph a few equations and then change the variable value and re-graph. For my previous labs, I have been copying the code and updating the values. However, I was wondering if it was possible to only update the variables and call a certain portion of the code with the updated values? Example:

% % Run portions of code after updating variables
a = 3; b = 7; x = linspace(0,200,1001);         % initial values

y = sin((a+x)/4) + b;                          % some equations
z = cos((b.*x)/50) + 2*a;

figure; 
plot(t, y, 'b', t, z, 'r'); ylim([4 9]);

% re-run code with a = 6 and b = 4
%       update values of a and b in this line
%       re-run lines 2-8 with updated a and b

Any help would be appreciated

Answer 1

[SK]

I ended up doing something similar to what Walter Roberson suggested, i.e. using a for loop. Initially, I wanted to get the plots into a subplot, but realized that would be too complicated. The code similar to what I did is below. (Note: I had to do three cases of tau and two cases of M).

for tau = [T, 5*T, 10*T]
    % computations of equations for three cases of tau
    for M = [M1, M2]
        % commutations for two cases of M
        % plot of equations
    end
end

Once executed the code, I ended up with six individual graphs. Once the code was published to PDF then everything looked alright. Using the for loop shortened my code from 200+ lines to just 30-something lines.

Answer 2

[Walter Roberson]

That is a major reason to code in functions and scripts: to be able to repeat code with different values.

[SK]

I understand that and I vaguely remember being able to do that in multiple .m files. However, my issue is that I have to submit everything as a single PDF file. That is why I wanted to have the whole code in one file. It has been quite some time since I took Intro to Matlab course so my memory is a little hazy. How do you suggest I do this?

[Walter Roberson]

   function lab7

     a = 3; b = 7;
     oops_I_did_it_again(a, b);
     a = 6; b = 4;
     oops_I_did_it_again(a, b);

   function oops_I_did_it_again(a, b)
    x = linspace(0,200,1001);         % initial values

    y = sin((a+x)/4) + b;                          % some equations
    z = cos((b.*x)/50) + 2*a;

    figure; 
    plot(t, y, 'b', t, z, 'r'); ylim([4 9]);

That is one single file.

You could also consider using a "for" loop.

for ab = [3 6; 7 4]
  a = ab(1); b = ab(2);
  x = linspace(0,200,1001);         % initial values

    y = sin((a+x)/4) + b;                          % some equations
    z = cos((b.*x)/50) + 2*a;

    figure; 
    plot(t, y, 'b', t, z, 'r'); ylim([4 9]);
  end

[SK]

Thank you. Although, when I try to run my code I am getting the following error:

function oops_I_did_it_again(a, b)

↑

Error: Function definitions are not permitted in this context.

I am not sure how to tackle this.

[Jiro Doke]

There was a typo in your original code. plot(t,y,... should be plot(x,y,...

Either way, create a single file (lab7.m) like this:

function lab7
a = 3; b = 7;
oops_I_did_it_again(a, b);
a = 6; b = 4;
oops_I_did_it_again(a, b);

function oops_I_did_it_again(a, b)
x = linspace(0,200,1001);         % initial values
y = sin((a+x)/4) + b;                          % some equations
z = cos((b.*x)/50) + 2*a;
figure;
plot(x, y, 'b', x, z, 'r'); ylim([4 9]);

Then run the code:

>> lab7