How to remove unwanted double image in plot

Hi Fellas

I created this plot from a text file I imported into matlab, and I am not sure why the plot looks like it has these extra lines on it, particularly one going straight from the starting point to the end poin on the graph. I am not sure why this plot has this issue, as I looked through the text file and all of the numbers seem correct. The plot was originally generated using a network analyzer on an antenna, and no double lines were originally present. I have also not seen this issue with any of the other plots I have made in matlab. Any info on what could be the issue is appreciated. I have attached the matlab code file and the s parameter data below.

Answer 1

[Matt J]

It is possible your points are not sorted in ascending order of x.

[Blayze]

Not sure what you mean by ascending order.

[Steven Lord]

Check that your data is sorted by calling issorted on the variable you're using as the X coordinates of your plot.

x = [1 2 3 4 5];
issorted(x, 'ascend') % true, x is in increasing order

ans = logical
   1

y = [1 2 3 4 5 1];
issorted(y, 'ascend') % false, y(6) is greater than y(5)

ans = logical
   0

[Matt J]

plot() connects your (x,y) points in whatever order they are listed, so, if they are not listed in consecutive order, you get things like this:

x=circshift(linspace(-1,0.75,50),-1); 
y=x.^2;

plot(x,y,'-o'); axis padded

[Blayze]

>> issorted(Simulated_data_elements_unconnected_frequency,'ascend')

ans =

logical

0

[Blayze]

Hmm it does look like that the x values are not in ascending order. Do you know how to check where the discontinuity is?

[Steven Lord]

Let's make some sample data:

x = [1 2 3 4 3 4 5 1]

x = 1×8

1 2 3 4 3 4 5 1

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ind = find(x(2:end) <= x(1:end-1))

ind = 1×2

4 7

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check = [x(ind); x(ind+1)].'

check = 2×2

4 3 5 1

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x(4) [the first element of ind] is indeed greater than x(5), as the first row of check shows. Similarly x(7) is greater than x(8) as shown in the second row of check.

[Blayze]

Thanks for the help everyone, it looks like one of the text files contained multiple sets of data, which is why the functions kept indicating the data for the x values was not always increasing. The plot now contains no extraneous lines.

Answer 2

[Image Analyst]

Try something like this with your data

[sortedx, sortOrder] = sort(x, 'ascend'); % Sort x and get the order it was sorted in.
sortedy = y(sortOrder); % Sort y the same way so the y stays matched up with its original x.
plot(sortedx, sortedy, 'b-', 'LineWidth', 2); % Plot the sorted data.