Finding the maximum of a function with vector variables

Hi all

I have two vectors x and y , which y is actually is a function of x , I wanted to find the extremum point of the function , I thought it's possible with fminunc but it didn't work , the error was that @myfun should be a function , how should I relate the two vectors and find the extremum point (here is a maximum)

the whole problem is also like this : we have x1,y1 that has one maximum (the function is a decreasing and is maximum at x1=0

then x2,y2 and ....xi,yi

then I have to plot another function that is the range that max(xi) changes within because x=0:0.1:xmax for every x vecor and for the y axis , a normalized of y/ymax for each xi,yi

please can you help me with a code ?