# How to find the slope of phase data (between two points) which is uneven

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Sriram Guddati on 12 Oct 2018
Answered: Greg Dionne on 26 Oct 2018 I have a phase vs frequency plot. I need to find the slope between point 'a' and point 'b' in an automated way instead of looking at the points 'a' and 'b' and calculating the slope. Can anyone help me with this?

Image Analyst on 12 Oct 2018
You ask ONLY about the slope, not about finding a and b, so I assume you've found "a" and "b" already. So, assuming your "a" is index1 and "b" is index2, you can do this
coefficients = polyfit(x(index1):x(index2), signal(index1:index2), 1);
slope = coefficients(1);
Sriram Guddati on 12 Oct 2018
Thank you, I will try this.

### More Answers (2)

jonas on 12 Oct 2018
Edited: jonas on 12 Oct 2018
I would suggest using either findpeaks to determine points a and b and then calculate the average slope or alternatively using findchangepts. If you want code, then I suggest you upload some data.
Sriram Guddati on 12 Oct 2018
Thanks, I will try this method

Greg Dionne on 26 Oct 2018
You could try a combination of unwrap (to remove the jumps of your array) and sgolay to do the differentiation. See the second example on how to perform differentiation.