Want to remove a line in my plot

Hi, pls I need to remove a straight line in my plot. I attached the two files ('A.txt' and 'B.txt') that I am analyzing. Could someone help out on this;

This is my code;

A=load('A.txt');B=load('B.txt');

X=(B(:,2)-A(:,2))/A(:,2);

plot(A(:,1),X, 'k');xlim([780 820])

Thank you

Answer 1

[Star Strider]

A = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/835480/A.txt');
A = A(:,[2 3]);
B = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/835485/B.txt');

X=(B(:,2)-A(:,2))./A(:,2);

figure
plot(A(:,1),X, 'k');
xlim([780 820])

It is not the same plot, and there is no horizontal line.

Since the data are probably in columns in the original plot as they are here, one option is:

AX = sortrows([A X],1)
A1 = AX(:,1)
X = AX(:,2)

figure
plot(A1, X, 'k');
xlim([780 820])

and see if that works, since it appears that the data are ‘wrapping’, and the sortrows call should eliminate that.

.

[Grace]

Hi, Star.

Thank you for your effort.

Thank you Benjamin. I think, the element wise operation is best for me because it preserves the shape the shape of my expected result. But by performing the element-wise operation, the true shape of the data is lost.

Th option of using 'sortrows' seems not to work too

So, I am still thinking on how to correct this error

[Star Strider]

My pleasure!

My apologies in suggesting element-wise operations, since that is not the problem.

The fact that only one column has non-zero entries is the problem —

A = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/835480/A.txt');
A = A(:,[2 3]);
B = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/835485/B.txt');

X=(B(:,2)-A(:,2))/A(:,2)

X = 2048×2048

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

findCol = find((~all((X==0),1)))

findCol = 1792

Xe = X(:,~all((X==0),1))                            % Only Column With Non-Zero Values

Xe = 2048×1

1.0e+00 * -0.0002 -0.0002 -0.0002 0.0001 0 0.0001 0.0001 0.0001 0.0002 0.0002

A1_0 = 1

figure
plot(A(:,1),Xe, 'k');
xlim([780 820])

Column 1792 is the only column that is not entirely 0, so plotting only it (‘Xe’ in my code in this Comment) eliminates the horizontal line at 0. I had to look carefully to find this information, and only understanding that element-wise operations are inappropriate here caused me to look for it.

.

[Grace]

Hi, Star.... Thank you very much

[Star Strider]

As always, my pleasure!

.

Answer 2

[Voss]

You should change the calculation of X to be:

X=(B(:,2)-A(:,2))./A(:,2);

This does element-wise division rather than matrix division.

If you check the size and value of X with the calculation the way you had it, you would see that X was a 2048-by-2048 matrix, so when you plot it against A(:,1), you are actually plotting 2048 lines, all but one of which are all zeros (the flat line).

With element-wise division, X is a column vector and one line is plotted, which is, I believe, what is intended.

[Grace]

Thank you Benjamin. I think, the element wise operation is best for me because it preserves the shape the shape of my expected result. But by performint the element-wise operation, the true shape of the data is lost.

So, I am still thinking on how to correct this error