Calculating the gradient at Gradient Ascent Algorithm

Hi, The code below is suppose to perform gradient ascent after implementation of the missing parts. There are several things I dont' know how to do, the first one being how to "Calculate the gradient at StartPt" which is suppose to be done in the for loop. I would very much appriciate help from you guys.

Thank you very much.

function GradientAscentEg

% plot the landscape
ezmesh(@ComplexLandscape,[-3 7],[-3 7])

% Enter maximum number of iterations of the algorithm, learning rate and
% mutation range
NumSteps=50;
LRate=0.1;
MaxMutate=1;

% TO DO: choose a random starting point with x and y in the range, (-2, 2)

GradAscent(StartPt,NumSteps,LRate);
% HillClimb(StartPt,NumSteps,MaxMutate);

function GradAscent(StartPt,NumSteps,LRate)
PauseFlag=1;
hold on;
for i = 1:NumSteps
  % TO DO: Calculate the 'height' at StartPt using SimpleLandscape

    % TO DO: Plot a point on the landscape in 3D 
    % use plot3(x,y,z,,'r*','MarkerSize',10)
    % to get a marker you can see well

    % TO DO: Calculate the gradient at StartPt

    % TO DO: Calculate the new point and update StartPoint

    % Make sure StartPt is within the specified bounds
    StartPt = max([StartPt;-2 -2]);
    StartPt = min([StartPt;2 2]);

    % Pause to view output
    if(PauseFlag)
        x=input('Press return to continue\nor 0 and return to stop pausing\n');
        if(x==0) PauseFlag=0; end;
    end
end
hold off

Answer 1

[Walter Roberson]

What is it that you are trying to take the gradient of? Is it the function handle @ComplexLandscape ? Is it @SimpleLandscape ? What are their input variables?

If you are trying to take the the numeric gradient of a function near the starting point, then you need to evaluate the function at 9 points total, all combinations of x0, x0-dx, x0+dx, y0, y0-dy, y0+dy . Then you can use gradient()

[N/A]

I need to calculate the gradient at a point and then use this gradient to update the point I'm at. SimpleLandscapeGrad returns the elements of the gradient as a vector.

[Walter Roberson]

Then it sounds like you just have to call SimpleLandscapeGrad and pass in the initial point.