Why do I have two waveforms in my plot while I should have only one?

I import a matrix from CST and plot 2 columns and get two different waveforms. Why is this happening since x and y are 360x1 columns?

[Mathieu NOE]

even if you data is 1D this could be a concatenation of two measurements , so you would also get 2 lines

make sure you have unique x and y

or maybe you already made a first plot with hold on and you still have this first trace

Answer 1

[Sandeep Mishra]

Hi Dimakopoulos,

I noticed from the attached screenshot that you have two input vectors, ‘x’ and ‘y’, each of size 360x1, resulting in two waveforms on your plot.

This situation often arises when the dataset used in the plot function contains duplicate value.

For instance, consider the following example:

x=[1,2,3,4,5,7,5,4,3,2]; 
y=[1,2,2,3,4,7,6,5,4,2]; 
plot(x,y) 

In this example, the point (2,2) is repeated, which can cause the plot to appear as if there are two waveforms.

To address this issue, you can remove the duplicate pairs of values from your dataset using the approach below:

% Pairing x and y values 
xy = [x', y']; 

% Find unique (x,y) pairs 
[unique_xy, unique_indices] = unique(xy, 'rows', 'stable'); 

% Extract the unique x and y values 
x_unique = unique_xy(:, 1); 
y_unique = unique_xy(:, 2); 

% Plotting the unique points 
plot(x_unique, y_unique)

Please refer to the below documentation to learn more about ‘unique’ function in MATLAB: https://www.mathworks.com/help/releases/R2020b/matlab/ref/double.unique.html

I hope this helps.