How to plot a matlab function for different parameters using hold on command

Question

I have a matlab function that contain some constant parameter, I want to draw that function, on say same figure, using hold on (probably) while changing the value of that constant. This my code:

close all
clear all
clc
m = 5;
x = 1:1:10;
y = m*x + 10;
h1 = figure;
plot(x,y)
m = 10;
figure(h1);
hold on
plot(x,y,': r')

When I tried using this code, I got two lines coincident on each others; and it looks matlab just used last value for the parameter m how can I make it use different values. I found some stuff here, but doesn't fulfill my needs. Any suggestions?

Robert Seifert · Accepted Answer · 2015-05-31 13:34:56Z

1

You need to recalculate y as well:

m = 5;
x = 1:1:10;
y = m*x + 10;

h1 = figure;
plot(x,y); hold on;

m = 10;
y = m*x + 10;

figure(h1);
plot(x,y,': r')

Or create an anonymous function:

x = 1:1:10;
f = @(m) m*x + 10;

%// and then:
h1 = figure;
plot(x,f(5)       ); hold on;
plot(x,f(10),': r');

answered May 31, 2015 at 13:34

Robert Seifert

25.3k13 gold badges75 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

AlFagera Over a year ago

all fine, however, in my actual situation, I want use that for PID control, where I've my parameters and ODE equations defined in one file (function file), and the parameters values and plots are defined in another m-file (the run file), you may check this for two links robot. Or should I post a new question? many thanks.

Robert Seifert Over a year ago

@AlFagera I cant open the link, but I'd guess it's definetely a new question.

AlFagera Over a year ago

@ thewaywewalk, Sorry for that; [this] (staff.kfupm.edu.sa/SE/mshahab/081_ee656_hw5_sol_shahab.pdf) , is the correct link.

Jim McAdams · Accepted Answer · 2015-05-31 14:01:41Z

0

Currently, you're only updating m but you also have to calculate y again. This is why it plots exactly the same y (i.e. m is still 5) function when you issue the second plot.

You might want to use a simple for loop for that, like:

m = 5;
x = 1:1:10;
figure;
hold on;
for m=1:1:10
    y = m*x + 10;
    plot(x,y,': r')
end

edited May 31, 2015 at 14:01

answered May 31, 2015 at 13:43

Jim McAdams

1,1041 gold badge15 silver badges30 bronze badges

2 Comments

AlFagera Over a year ago

if I want to make legend in this case using for loop, how it'll work.

Jim McAdams Over a year ago

.. see my other answer.

Community · Accepted Answer · 2017-05-23 12:06:01Z

In addition to the short answer - improving the plot..

    %% Data Preparations
    x = 1:10;
    ms = 3;             % number of different slopes

    %% Graph Preparations
    hold on;

    % Prepare the string cell array
    s = cell(1, ms);

    % Handle storage
    h = zeros(1, ms);

    % Plot graphs
    for m=1:ms
        y = m*x + 10;
        h(m)= plot(x,y,'Color',[1/m rand() rand()]);
        s{m} = sprintf('Plot of y(m=%d)', m);
    end

    % Plot all or select the plots to include in the legend
    ind = [ms:-1:1] .* ones(1,ms);  % plot all
    %ind = [ 1 3 4 ];               % plot selected

    % Create legend for the selected plots
    legend(h(ind), s{ind});

Additional advice: When working with MATLAB and you try to improve the performance of your code, you shoud try to avoid using for-loops since MATLAB is MATrix manipulation and that's what it can do best. Ones you've taken this philosophy in, you'll create the most beautiful code one-liners! ;)

This script is an adoption of Steve Lord's post.

Collectives™ on Stack Overflow

How to plot a matlab function for different parameters using hold on command

3 Answers 3

3 Comments

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related