Finding the turning points

Hi i want to ask about something, i want to solve and locate the turning points (maximum and minimum point) of a graph using matlab gui but i dont know how to code it. The function is user defined and here is my code:

funcString = get(handles.edit1,'String'); 
  funcHandle = str2func(['@(x)' funcString]); 
  x = linspace(10,-10,100); 
  y = funcHandle(x);
  plot(handles.axes1,x,y); 

[Torsten]

So you want to determine minima and maxima of the first derivative of your "funcHandle" ?

[Reynand Joe]

yess

[Image Analyst]

Answer 1

[John D'Errico]

If all you will use are the 100 coarsely sampled points you are plotting, then min and max will do what you want. Look at the second arguments returned from min and max. You could also use findpeaks.

If you are willing to use the function itself, then you might use fminbnd. Note that fminbnd always searches fro a minimum. But you could then search for the minimum of -f(x), which would be the maximum of f.

[Reynand Joe]

Hi can you make me a code using this? I'm still at beginner level as matlab user and i dont have any idea how to code that

[Image Analyst]

Did you look up min and max in the help? That would be the first step. Using your existing numerical array, "y", do this:

maxYValue = max(y)
minYValue = min(y)