Trouble graphing. My function is not appearing.

x = linspace(0,10,100)

y = (2+x)/(2-x)

plot (x, y)

Answer 1

[Sam Chak]

Hi @Alex Chen

If you want to see the asymptote, perhaps use fplot() instead.

https://www.mathworks.com/help/matlab/ref/fplot.html

fplot(@(x) (2+x)./(2-x), [0 4])

Answer 2

[Voss]

Use element-wise division (./).

With matrix division (/) y is a scalar, and plotting a scalar y vs a vector x creates one line for each element of x, but each line contains only one point, so you can't see them without a data marker:

x = linspace(0,10,100);
y = (2+x)/(2-x) % y is a scalar: plot makes a line for each x value

y = -1.6856

plot (x, y, '.') % plot with a marker to see the lines

Using element-wise division makes y a vector the same size as x, so you get one line, as intended:

figure()
y = (2+x)./(2-x) % y is a vector

y = 1×100

1.0000 1.1064 1.2247 1.3571 1.5063 1.6757 1.8696 2.0938 2.3559 2.6667 3.0408 3.5000 4.0769 4.8235 5.8276 7.2500 9.4211 13.1429 21.0000 48.5000 -199.0000 -34.0000 -19.0000 -13.3750 -10.4286 -8.6154 -7.3871 -6.5000 -5.8293 -5.3043

plot (x, y)

[Alex Chen]

Thanks, that makes sense! But it doesn't seem to match with the same function graphed on desmos as it shows an x=2 asymptote, and the matlab veresion has a line joing the function and making it continuous?

[Image Analyst]

Change your x range

x = linspace(-15, 15, 1980);
y = (2+x)./(2-x) % y is a vector
% Make middle invisible.
[~, index] = min(abs(x-2));
y(index) = nan;
ylim([-15, 10]);