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

Question

SK 2016-12-7

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回答： SK 2016-12-11

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

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Answer 1

SK 2016-12-11

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在 MATLAB Online 中打开

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.

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Answer 2

Walter Roberson 2016-12-7

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

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SK 2016-12-7

编辑：SK 2016-12-7

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 2016-12-7

在 MATLAB Online 中打开

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]);