Finding Peaks and Troughs of a signal using differentiation?

Hi,

Firstly, I do know how to find the peak and troughs using findpeak blackbox. And now am trying to write my own algorithm to understand the Mathematics behind finding peaks and troughs in a signal . Obviously ,I used differentiation to find the local minima and maxima . The signal is a PPG signal .However, this method also detects unwanted peaks and troughs at the position of notch and I'm facing trouble in eliminating it .

The code and the figure are here below.

Any suggestions or inputs on this that can help me in getting rid of this unwanted peaks and troughs would be highly appreciated .

Thankyou

[madhan ravi]

Have you looked into islocalmax() and it’s relatives?

[Suvvi Kuppur Narayana Swamy]

Yes I have .islocalmax and find peaks are working fine in detecting the peaks and troughs.But I want to understand using the differentiation technique .