how to extract the time interval where variables start to increase

i have a function and i plot for every moment results of this function, such the image indicate, ,and then i want to detect the moment where variables start to increase and stop increasing

Answer 1

[Image Analyst]

Try this:

indexes = find(signal < -50);

That will tell you whenever an signal value is less than -200. If you want to find only stretches where it meets the condition for some minimum number of elements, you can use bwareaopen() to throw out short stretches.