# Why is my function not graphing in the plot?

38 vues (au cours des 30 derniers jours)
Aarya O le 18 Juin 2022
Commenté : Voss le 18 Juin 2022
I am trying to plot a basic function in MATLAB, and the plot is appearing in a figure window, but these is no graph in the plot. My previous question was regarding the same issue, but the error was in my faulty understanding of linspace. I don't believe I am making the same mistake with linspace. I have pasted my code below as well as the plot generated by the code. I verified the shape of the plot with a graphing calculator to make sure I was using the correct x and y limits.
Code:
%Transfer Function for a passive, first-order, high-pass filter: 1/wRC
x = linspace(0.01,1,100);
%For this example, let's set R = 1 kOhm and C = 1 uF
%The variable x represents angular frequency w
R = 1000;
C = 0.000001;
g = (sqrt(R.^2 * x.^2 * C.^2))/(sqrt(1 + (R.^2 * x.^2 * C.^2)));
y = -20*log10(g);
plot(x,y);
grid on
xlim([0 0.05]);
ylim([0 0.05]);
Plot: I am new to MATLAB and still learning, so thank you again for your time, and I appreciate any guidance you guys can give me.
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### Réponse acceptée

Star Strider le 18 Juin 2022
Two problems:
First, you need to do element-wise division:
g = (sqrt(R.^2 * x.^2 * C.^2))./(sqrt(1 + (R.^2 * x.^2 * C.^2)))
↑ ← HERE
and second, the values of the curve are much greater than the ylim values set for them.
Also, using a logarithmic axis for the independent variable might make the plot look a bit closer to what you want.
%Transfer Function for a passive, first-order, high-pass filter: 1/wRC
x = linspace(0.01,1,100);
%For this example, let's set R = 1 kOhm and C = 1 uF
%The variable x represents angular frequency w
R = 1000;
C = 0.000001;
g = (sqrt(R.^2 * x.^2 * C.^2))./(sqrt(1 + (R.^2 * x.^2 * C.^2)));
y = -20*log10(g);
plot(x,y);
grid on % % xlim([0 0.05]);
% % ylim([0 0.05]);
% set(gca, 'XScale','log') % Optional
.
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Star Strider le 18 Juin 2022
As always, my pleasure!

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### Plus de réponses (1)

Voss le 18 Juin 2022
Modifié(e) : Voss le 18 Juin 2022
Just like you use element-wise operations .* and .^ for multiplication and exponentiation, respectively, you must also use element-wise division ./
x = linspace(0.01,1,100);
%For this example, let's set R = 1 kOhm and C = 1 uF
%The variable x represents angular frequency w
R = 1000;
C = 0.000001;
g = (sqrt(R.^2 * x.^2 * C.^2))/(sqrt(1 + (R.^2 * x.^2 * C.^2))) % matrix division / gives a scalar
g = 5.0500e-04
g = (sqrt(R.^2 * x.^2 * C.^2))./(sqrt(1 + (R.^2 * x.^2 * C.^2))) % element-wise division ./ gives a vector the same size as x
g = 1×100
1.0e-03 * 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0700 0.0800 0.0900 0.1000 0.1100 0.1200 0.1300 0.1400 0.1500 0.1600 0.1700 0.1800 0.1900 0.2000 0.2100 0.2200 0.2300 0.2400 0.2500 0.2600 0.2700 0.2800 0.2900 0.3000
y = -20*log10(g);
plot(x,y);
grid on (Also, these xlim and ylim don't make sense if you want to see the plotted line.)
% xlim([0 0.05]);
% ylim([0 0.05]);
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Voss le 18 Juin 2022
You're welcome!

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