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matlabplotmatlab-figure

Animated Discrete Stem Plot

So I want to create an animated plot of a discrete-time complex exponential function. The simplest non-animated plot would be given by this:

n=-5:40;
x=(exp((3*4j)*n)).*(n>=0);
y=real(x);
subplot(2,1,1);
stem (n,y)
z=imag(x);
subplot(2,1,2);
stem (n,z)

How do I animate it to show the function for the different numbers of samples considered in a given interval (assuming I have a time interval specified by start second and end second and a vector containing the number of sample values in the given interval)?

I tried along these lines:

figure,hold on
xlim([min(x(:)) max(x(:))])
ylim([min(y(:)) max(y(:))])

%// Plot point by point
for k = 1:numel(x)
    stem (k,y) %// Choose your own marker here
    pause(0.001);     
end

That doesn't compile. How to achieve this?

Solution

  • Short answer:

    Make the following two changes:

    ① Replace xlim([min(x(:)) max(x(:))]) with this xlim([1 numel(x)]).
    ② Replace stem (k,y) with this: stem (k,y(k)).

    Detailed Answer:

    ① xlim([min(x(:)) max(x(:))]) is giving you the following error:

    Error using matlab.graphics.axis.Axes/set
While setting the 'XLim' property of 'Axes':
This is not a valid LimitsWithInfs value. Complex inputs are not supported

    The error message tells you exactly what the problem is. Your vector x contains complex numbers. Time axis having complex numbers also doesn't imply anything.
    It seems that you would want to replace this line xlim([min(x(:)) max(x(:))]) with this:
    xlim([1 numel(x)]).

    ② Inside the loop, stem (k,y) is giving you this error:

    Error using stem (line 46)
X must be same length as Y.

    The error message tells you exactly what the problem is. Here k is just a scalar (1x1) but y is a 1x46 vector.
    Since you want to plot y point by point, replace stem (k,y) with this: stem (k,y(k)).

    Output after making the mentioned fixes:

    Output