Plotting a unit step function without heaviside.
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Hannah Chamberlain
le 4 Fév 2017
Réponse apportée : Sam Chak
le 17 Juil 2024 à 22:21
So for my class I need to be able to plot
Xg(t)= u(t+1)-2u(t-1)+u(t-3)
Xh(t)=(t+1_u(t-1)-tu(t)-u(t-2)
and a whole other host of things but for these ones I'm confused on how to do it without the heaviside function. I got an answer for just u(t) was:
t = (-1:0.01:5)';
unitstep = t>=0;
plot(t,unitstep)
This worked.
When I tried to get it to shift instead the line became more of a ramp function.
t = (-1:0.01:5)';
unitstep = t>=0;
u1 = unitstep.*(t+1)
plot(t,u1)
What am I doing wrong?
2 commentaires
Adam Turton
le 3 Oct 2019
Matlab has an issue with jump discontinuities, so 0.01 makes it so that it "updates" the function to the correct placement, allowing what would otherwise plot as a ramp function to show as a near vertical line.
Réponse acceptée
Chad Greene
le 4 Fév 2017
Modifié(e) : Chad Greene
le 4 Fév 2017
Hi Hannah,
Your unitstep contains only zeros and ones. So when you plot
plot(t,unitstep)
it's a Heaviside function, just as you expect. But when you multiply unitstep by t, you end up plotting zeros wherever unitstep is zero, and the values of t (not ones!) wherever unitstep is one. If you're trying to move a simple Heaviside function left or right, try this:
t = (-1:0.01:5)';
% Start with all zeros:
unitstep = zeros(size(t));
% But make everything corresponding to t>=1 one:
unitstep(t>=1) = 1;
plot(t,unitstep,'b','linewidth',3)
% Repeat, with everything shifted to the right by 1 unit:
unitstep2 = zeros(size(t));
unitstep2(t>=2) = 1;
hold on
plot(t,unitstep2,'r:','linewidth',2)
box off
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/176999/image.png)
5 commentaires
Chad Greene
le 7 Fév 2017
Perhaps you wanted to multiply the unitsteps together rather than add them?
Plus de réponses (3)
Les Beckham
le 6 Fév 2017
You are very close to the first half of your goal.
Your line of code
Ut= unitstep+unitstep2+unitstep3;
should, I believe, reflect what you are calling Xg in your original problem. You might want to rename it to help you remember the connection between the code and the original equation. Also, you need to look at what the multipliers/coefficients are in your original Xg definition. u(t-1), which you are calling unitstep2 in your code, is multiplied by -2 when assembling the total Xg. This is not reflected in your code.
I think you can figure it out from here.
2 commentaires
abdelkader omr
le 17 Juil 2024 à 20:52
I want to plot a unit step function
x axis represenets time and its value [0 1 2 3 4 5 6 7]
y axis represents load and its value are[2 2 3 3 3 3 2 2]
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Sam Chak
le 17 Juil 2024 à 22:21
Your function looks somewhat like a Boxcar function. However, your description of the continuous-time function is slightly unclear because they are discrete values. There are simpler methods for continuous-time, but since yours are discrete values, perhaps you may consider flexibly creating the function as follows:
%% Boxcar function
function y = boxcar(x, params)
for i = 1:length(x)
if x(i) <= params(1)
y(i) = 2;
elseif x(i) <= params(2)
y(i) = 2;
elseif x(i) <= params(3)
y(i) = 2;
elseif x(i) <= params(4)
y(i) = 3;
elseif x(i) <= params(5)
y(i) = 3;
elseif x(i) <= params(6)
y(i) = 3;
elseif x(i) <= params(7)
y(i) = 2;
elseif x(i) <= params(8)
y(i) = 2;
else
y(i) = 2;
end
end
end
%% Plot the function
x = linspace(0, 10, 1001);
y = boxcar(x, [0 1 2 3 4 5 6 7]);
plot(x, y, 'linewidth', 2), grid on, ylim([1 4])
xlabel('Time'), ylabel('Load'), title('Boxcar function')
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