Calculating the gradient at Gradient Ascent Algorithm

6 次查看（过去 30 天）
N/A
N/A 2016-11-7
评论： Walter Roberson 2016-11-7
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

请先登录，再回答此问题。

回答（1 个）

Walter Roberson
Walter Roberson 2016-11-7
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()
  2 个评论
N/A
N/A 2016-11-7
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
Walter Roberson 2016-11-7
Then it sounds like you just have to call SimpleLandscapeGrad and pass in the initial point.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Simulation 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by