Spikes in my heaviside function/step functions

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Samantha Zhao
Samantha Zhao 2019-2-26
评论： Samantha Zhao 2019-3-7
I am trying to plot a simple unit step function (below) using the heaviside function.
x(t) =u(t)−u(t−2)
t = -10:.01:10;
x = heaviside(t) - heaviside(t-2);
plot(x)
The plot results in a unit step function with spikes at 4 and -3.
heavisideSpikes.png
So far my solutions have been editing in the correct values at the appropriate indexes, but it has been getting very tedious. What could be causing this issue? I am also using the 2018b edition and have not noticed this in previous versions.
  2 个评论
Asad Mirza
Asad Mirza 2019-2-26
编辑：Asad Mirza 2019-2-26
Not sure why but when I run the code it comes out without any strange spikes. I am also using MATLAB 2018b.
Just checked it with both MATLAB Online and Octave and I get the same results
Matlab Online.PNG
Octave Online.PNG
Walter Roberson
Walter Roberson 2019-3-1
Also, be careful about what heaviside(0) means. See sympref('HeavisideAtOrigin')

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回答（1 个）

Munish Raj
Munish Raj 2019-3-1
Hello Samantha,
The plot in your picture is a mixture of two different plots. It has the intended heaviside as expected.
As you can notice, the y axis of the plot is from [-3 4]. However, the expected heaviside function is plotted in [1 0] on the y axis.
Also please make sure there is no previous plot.
Use the hold off command before plotting the heaviside function.
hold off
to make sure that a new plot is being plotted.
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Munish Raj
Munish Raj 2019-3-7
heavisideSpikes.png
The red highlighted plot is the heaviside plot that you are looking for.
The other parts are the extra plots, possibly from another plot function.
Samantha Zhao
Samantha Zhao 2019-3-7
I have reinstalled Matlab, opened up a new script, and made sure that there is nothing else being plotted with my heaviside. I'm really at a loss expecially when others are able to produce a normal graph with the exact code!

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