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

Question

Sriram Guddati 2018-10-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423685-how-to-find-the-slope-of-phase-data-between-two-points-which-is-uneven

回答： Greg Dionne 2018-10-26

untitled.png

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?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2018-10-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423685-how-to-find-the-slope-of-phase-data-between-two-points-which-is-uneven#answer_341108

在 MATLAB Online 中打开

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);

3 个评论
显示 1更早的评论隐藏 1更早的评论

Image Analyst 2018-10-12

在 MATLAB Online 中打开

OK, that wasn't stated in the original question. So you can use

[peakValues, indexOfPeaks] = findpeaks(signal);
[valleyValues, indexOfValleys] = findpeaks(-signal);
valleyValues = -valleyValues; % Flip again to get right side up.

Of course you will find lots of peaks and lots of valleys so you'll have to decide which to concentrate on.

Sriram Guddati 2018-10-12

Thank you, I will try this.

请先登录，再进行评论。

Answer 2

jonas 2018-10-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423685-how-to-find-the-slope-of-phase-data-between-two-points-which-is-uneven#answer_341101

编辑：jonas 2018-10-12

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.

3 个评论
显示 1更早的评论隐藏 1更早的评论

jonas 2018-10-12

在 MATLAB Online 中打开

Yes of course. The index is the second output of findpeaks. Note that you need to run the function two times, one for peaks and one for valleys. For the latter, you just turn the plot upside down, i.e.

findpeaks(-y)

Sriram Guddati 2018-10-12

Thanks, I will try this method

请先登录，再进行评论。

Answer 3

Greg Dionne 2018-10-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423685-how-to-find-the-slope-of-phase-data-between-two-points-which-is-uneven#answer_343670

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.