I'm having trouble writing this function can anyone help?

Chapter 15 #5

Mathematically speaking, a critical point occurs when the derivative of a function equals zero. It is possible that a local minimum or a local maximum occurs at a critical point. A local minimum is a point where the function's value to the left and right of it are larger, and a local maximum is a point where the function's value to the left and right are smaller.

Write a function that finds the local minimum and local maximum points. Call the function findPoints. It should take in a vector of x values and a vector of y values and return two vectors:

the first vector should contain the x values where the minimum points occur

the second vector should contain the x values where the maximum points occur. You may assume that the local minimums and maximums occur at integer values. This will take care of any decimals created when using diff.

Example:

x = linspace(-5, 5, 1000); y = x.^3 -12*x; [min max] = findPoints(x, y) should return min = 2 max = -2

[Steven Lord]

Please show how far you've gotten in writing your own findPoints function and ask a SPECIFIC question about where you're stuck.

[jose sanchez]

 function [min max] = find_points(x, y)
    min = [];
    max = [];
   for i = locat
   %         x = findZero(x(i), x(i+1));
           if f((i-1)) > f(i)
               if f((i+1)) > f(i)
                 min = [min x(i)]
               end
           else
               max = [max x(i)]

           end

       end

[Walter Roberson]

What is "locat" ?

[Walter Roberson]

It is firmly recommended that you never name a variable "min" or "max" as doing so interferes with using the MATLAB routines of those names, and makes it more difficult for other people to read the code.

Answer 1

[Image Analyst]

Try

for k = 2 : length(y)-1
    if y(k) > y(k-1) && y(k) > y(k+1)
        % It's a local max
    elseif y(k) < y(k-1) && y(k) < y(k+1)
        % It's a local min
    end
end

See if you can finish the rest of the code to store the index k as a max or min, and to get the x values there.