Finding the Maximum Value

Hello, I currently have a set of data that I use f = fit(x,y,'gauss2') to find the best gaussian curve fit. Next, I want to find the full width half maximum value, however I am having trouble doing this. Currently, my data is loaded as an array with x values in the first column and y values in the second. Is there any way to load the array and then find the full width half max value?

Second, I am also simply trying to find the max value of the curve that is the best fit. Therefore, after I find f (the best fit), I am trying to find max(f). However, since the value is not an integer, matlab is returning an error message: Subscript indices must either be real positive integers or logicals. Is there any way around this so that I can find the value of the max peak of the curve of best fit. Any help would be greatly appreciated, thank you!