how to plot split function in MATLAB

Question

I am trying to plot ONE graph in MATLAB that has two functions that take different domains.

f1(t) = 50*t              % 0<=t<15
f2(t) = 160/3)*t - 180    % 15<=t<=60

I tried using below

t1 = 0:15;
y = f1(t1)
plot(t1,y)
hold on

t2 = 15:60 ;
y = f2(t2)
plot(t2,y)
hold off

then I get TWO graphs that do not form a continuous line. the graph from the above code

I need the red graph starting at (15,750) I can cheat and move the starting point for the second graph to be (15,750) but is there a way I can graph these as one function?

Wolfie · Accepted Answer · 2021-06-18 07:07:47Z

0

One option is to define a single function where each term is multiplied by the condition for t, effectively zeroing it out when not applicable

f = @(t) (50*t).*(t<15) + ((160/3)*t - 180).*(t>=15);

t = 0:60;
plot( t, f(t) );

If your functions are complex then this could become slightly hard to read, but it's compact.

answered Jun 18, 2021 at 7:07

Wolfie

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2 Comments

Kumi Over a year ago

Thank you for your help! It's my first question on StackOverflow, I didn't expect to get the input this soon. Your code looks very nice too ;-;

Kumi Over a year ago

This did the job! Thank you so much!

Siva Srinivas Kolukula · Accepted Answer · 2021-06-18 04:40:57Z

0

Two methods. Using loop and without loop.

f1 = @(t) 50*t              % 0<=t<15
f2 = @(t) 160/3*t - 180    % 15<=t<=60

t = 0:60 ; 
f = [f1(t(t<15)) f2(t(t>=15))] ;
plot(t,f)

With loop

f1 = @(t) 50*t              % 0<=t<15
f2 = @(t) 160/3*t - 180    % 15<=t<=60
f = zeros(size(t)) ;
for i = 1:length(t)
    if t(i) < 15
        f(i) = f1(t(i)) ;
    else
        f(i) = f2(t(i)) ;
    end
end
plot(t,f)

answered Jun 18, 2021 at 4:40

Siva Srinivas Kolukula

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1 Comment

Kumi Over a year ago

Thank you so much! It looks a lot nicer in your first solution compared to mine :D

Kumi · Accepted Answer · 2021-06-18 07:27:28Z

0

I realized that I needed to make the domain uniform.

%setting domain t (0 <= t <15 and 15 <= t)
t = [0:30]; %suppose match time is 30 seconds

t1 = t(1:16);
t1(numel(t)) = 0; %f1 takes t1 as domain (0 <= t < 15):array 17-31 is filled with 0

t2 = t(16:31);
t2 = [zeros(1, max(0, 15)), t2];  %f2takes t2 as domain (15 <= t):array 1-16 is filled with 0
t2(1:16) = 15;   %array 0-16 is filled with 15, to cancel (t-15) in the function 

f= f1(t1) + f2(t2); %Moira's dmg from two domains are added to form one data set

plot(t,f, 'm--') %plotting f

here is my end result using the method above

I still need to get my domains correct I think. The graph doesn't look as it is supposed to hahaha

edited Jun 18, 2021 at 7:27

answered Jun 18, 2021 at 7:10

Kumi

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2 Comments

Wolfie Over a year ago

It is conventional to edit your original question if the scope changes or it needs clarifying, otherwise existing answers can become obsolete

Kumi Over a year ago

@Wolfie I didn't mean to make things complicated, I'm not quite familiar with how StackOverflow works. Thank you for letting me know!

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