# Making ramp and unit step function in MATLAB

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Steven Franzkowiak on 2 Oct 2017
Answered: Sajib Biswas Shuvo on 26 Jul 2021
I am having trouble writing the code for these step functions. I would appreciate any help. I am using MATLAB version 9.3.0.701794 (R2017b)
Ramnarayan Krishnamurthy on 4 Oct 2017

Robert U on 5 Oct 2017
Edited: Robert U on 5 Oct 2017
Hello Steven Franzkowiak,
one solution is to write a function that behaves as the plotted function. One can argue about the points at t = 4 and t = 8 since they are not defined uniquely. I suppose f(t=4) = 0 and f(t=8) = -2.
The function can look like the following code. Matlab 2017b supports piecewise definition as can be found in one of the links posted by Ramnarayan Krishnamurthy.
function [ vec_out ] = hw_piecewise_R2014b( vec_in )
% support column/row vectors
if size(vec_in,1) > 1
vec_in = vec_in';
transpose_vec = 1;
else
transpose_vec = 0;
end
% everywhere else function returns zero
vec_out = zeros(1,size(vec_in,2));
% defined sections of function as seen from chart
vec_out(vec_in >= -6 & vec_in <= 0) = 5/6 * vec_in(vec_in >= -6 & vec_in <= 0) + 5;
vec_out(vec_in > 0 & vec_in <= 4) = -5/4 * vec_in(vec_in > 0 & vec_in <= 4) + 5;
vec_out(vec_in > 4 & vec_in <= 8) = -2;
% return vector according to input
if transpose_vec
vec_out = vec_out';
end
end
Having that function you must define a vector t and call the four versions:
t = -10:0.01:10;
f1 = hw_piecewise_R2014b(t);
figure; plot(t,f1)
f2 = hw_piecewise_R2014b(-t);
figure; plot(t,f2)
f3 = hw_piecewise_R2014b(t-4);
figure; plot(t,f3)
f4 = hw_piecewise_R2014b(2*t - 4)
figure; plot(t,f4)
f5 = hw_piecewise_R2014b(-t/2 - 4)
figure; plot(t,f5)
Kind regards,
Robert
##### 2 CommentsShowHide 1 older comment
Robert U on 5 Oct 2017
Thank you for your comment, Jan Simon. I decided to post my solution despite the drawback you describe.
In my opinion, the implicit link to logical indexing and functions are valuable for other readers as well and outweigh the drawback that Steven could accomplish his homework by copying the full solution.
Kind regards,
Robert

Sajib Biswas Shuvo on 26 Jul 2021
This code does the job too. It uses the Symbolic Math toolbox.
syms t;
f_negative_t = 5*heaviside(-t) -5/6 * (-t) * heaviside(-t ) ...
+ 5/6 * (-t-6) * heaviside(-t -6);
f_positive_t = +5*heaviside(t) - 5/4 *t* heaviside(t) ...
- 2*heaviside(t-4) + 5/4*(t-4)*heaviside(t-4)...
+ 2*heaviside(t-8);
f = f_positive_t + f_negative_t;
fplot(f,[-7,10]);
xline(0), yline(0);

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