How to find a slope of signal if we do not know the value of x1, x2, y1, y2

How can we find the slope of a signal if we do not know the value of x1, x2, y1, y2

which we cannot use

Slope = (y2 - y1) / (x2 - x1);

Example:

load sunspot.dat

year = sunspot(:,1);
avSpots = sunspot(:,2);

[pks,loc]=findpeaks(avSpots,year, 'Annotate','extents','WidthReference','halfheight')
axis([1700 1711 0 100])

give a graph of

Thank you

Answer 1

[Star Strider]

I am not certain what you intend by ‘slope of a signal’. You can easily determine the derivatives of the signal with the gradient (link) function.

[Matlaber]

Thanks.

I mean I want the slope of the signal in the below draw area.

Black colour line.

[Star Strider]

I do not have the signal you are plotting, however the slope (and intercept) are easy enouigh to determine:

x = [925 1075];
y = [5 20];
B = [x(1) 1; x(2) 1]\[y(1); y(2)];
Slope = B(1)
Slope =
    0.1000   

If you determine the ‘peaks’ and ‘valleys’ using findpeaks, it should be relatively straightforward to calculate the slopes you are interested in.

[Matlaber]

Thanks.

i can use the peak value as my Y2 which is easier than checking the graph value.

Can I know what you mean by ‘Valley’? Is it ’locs’ in findpeaks?

How about value of Y1?

[Star Strider]

My pleasure.

A ‘valley’ is the trough between peaks, given by the respective values of ‘-pks’ (the amplitude) and ‘locs’ (position) of the inverted signal.

the ‘y(1)’ value is the trough (negative ‘peak’ of the inverted signal), and ‘x(1)’ would be the respective ‘locs’ value of the same signal at the same point.

[Matlaber]

Thanks a lot!

[Star Strider]

As always, my pleasure!