# Issue regarding a data plot

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Rahul
on 8 Aug 2024

Commented: Divyajyoti Nayak
on 8 Aug 2024 at 10:09

Hi,

I have a data as attached herewith.

The blue plot represents the gradient while the orange plot represents the percentage difference between the two datapoints.

But as you can see that at distance 0.2 the orange plot shoots up although the blue plot is sufficiently smooth.

I don't see any noise or outliers present at that point.

Can you advice me a way how to correct the percentage profile in this case?

##### 2 Comments

Divyajyoti Nayak
on 8 Aug 2024

Edited: Divyajyoti Nayak
on 8 Aug 2024

### Accepted Answer

Divyajyoti Nayak
on 8 Aug 2024

Hi Rahul, I think the reason your graph shoots up so suddenly is due to the way you have defined the ‘percentage_difference_gI’ vector.

percentage_difference_gI(i) = abs(Normalized_intensity_gradient(end,i+1)-Normalized_intensity_gradient(end,i))*200/abs(Normalized_intensity_gradient(end,i+1)+Normalized_intensty_gradient(end,i));

At distance 0.2, the gradient intensity is very close to 0. It is possible that the gradient intensity is crossing over from positive to negative. If this is the case then the numerator of your percentage will become larger than the denominator. For example,

Normalized_intensity_gradient(end,i+1) = 0.015;

Normalized_intensity_gradient(end,i) = -0.01;

percentage_difference_gI(i) = abs(0.015 – (-0.01))*200/ abs(0.015 + (-0.01));

percentage_difference_gI(i) = 0.025*200/0.005 = 1000

Here’s some code to show this visually with some dummy data:

data = -0.2:0.01:0.2;

percentage = abs(data(2:end)-data(1:end-1))./abs(data(2:end)+data(1:end-1));

percentage = percentage * 200;

plot(data(2:end),percentage);

##### 0 Comments

### More Answers (1)

Rahul
on 8 Aug 2024 at 9:50

##### 1 Comment

Divyajyoti Nayak
on 8 Aug 2024 at 10:09

Hey @Rahul, I'm not sure what your aim is exactly. Your expression for percentage difference is finding the percentage with respect to the average of 2 data points not the percentage increase from one data point to another. According to me, a simple percentage expression would be something like this:

percentage_difference_gI = (Normalized_intensity_gradient(end,2:end)-Normalized_intensity_gradient(end,1:end-1))./Normalized_intensity_gradient(end,1:end-1);

percentage_difference_gI = abs(percentage_difference_gI)*100;

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