Machine-learning-ex8
这是Coursera上 Week9的ml-ex8的编程作业代码。经过测验,全部通过。
具体文件可以进入我的github
包括以下3个文件:
% estimateGaussian.m
% selectThreshold.m
% cofiCostFunc.m
estimateGaussian.m
function [mu sigma2] = estimateGaussian(X)
%ESTIMATEGAUSSIAN This function estimates the parameters of a
%Gaussian distribution using the data in X
% [mu sigma2] = estimateGaussian(X),
% The input X is the dataset with each n-dimensional data point in one row
% The output is an n-dimensional vector mu, the mean of the data set
% and the variances sigma^2, an n x 1 vector
%
% Useful variables
[m, n] = size(X);
% You should return these values correctly
mu = zeros(n, 1);
sigma2 = zeros(n, 1);
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the mean of the data and the variances
% In particular, mu(i) should contain the mean of
% the data for the i-th feature and sigma2(i)
% should contain variance of the i-th feature.
%
mu=sum(X)/m;
sigma2=sum((X - mu) .^ 2)/m;
% =============================================================
end
selectThreshold.m
function [bestEpsilon bestF1] = selectThreshold(yval, pval)
%SELECTTHRESHOLD Find the best threshold (epsilon) to use for selecting
%outliers
% [bestEpsilon bestF1] = SELECTTHRESHOLD(yval, pval) finds the best
% threshold to use for selecting outliers based on the results from a
% validation set (pval) and the ground truth (yval).
%
bestEpsilon = 0;
bestF1 = 0;
F1 = 0;
stepsize = (max(pval) - min(pval)) / 1000;
for epsilon = min(pval):stepsize:max(pval)
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the F1 score of choosing epsilon as the
% threshold and place the value in F1. The code at the
% end of the loop will compare the F1 score for this
% choice of epsilon and set it to be the best epsilon if
% it is better than the current choice of epsilon.
%
% Note: You can use predictions = (pval < epsilon) to get a binary vector
% of 0's and 1's of the outlier predictions
predictions=(pval<epsilon);
tp=sum((predictions==1)&(yval==1));
fp=sum((predictions==0)&(yval==1));
fn=sum((predictions==1)&(yval==0));
prec=tp/(tp+fp);
rec=tp/(tp+fn);
F1=2*prec*rec/(prec+rec);
% =============================================================
if F1 > bestF1
bestF1 = F1;
bestEpsilon = epsilon;
end
end
end
cofiCostFunc.m
function [J, grad] = cofiCostFunc(params, Y, R, num_users, num_movies, ...
num_features, lambda)
%COFICOSTFUNC Collaborative filtering cost function
% [J, grad] = COFICOSTFUNC(params, Y, R, num_users, num_movies, ...
% num_features, lambda) returns the cost and gradient for the
% collaborative filtering problem.
%
% Unfold the U and W matrices from params
X = reshape(params(1:num_movies*num_features), num_movies, num_features);
Theta = reshape(params(num_movies*num_features+1:end), ...
num_users, num_features);
% You need to return the following values correctly
J = 0;
X_grad = zeros(size(X));
Theta_grad = zeros(size(Theta));
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the cost function and gradient for collaborative
% filtering. Concretely, you should first implement the cost
% function (without regularization) and make sure it is
% matches our costs. After that, you should implement the
% gradient and use the checkCostFunction routine to check
% that the gradient is correct. Finally, you should implement
% regularization.
%
% Notes: X - num_movies x num_features matrix of movie features
% Theta - num_users x num_features matrix of user features
% Y - num_movies x num_users matrix of user ratings of movies
% R - num_movies x num_users matrix, where R(i, j) = 1 if the
% i-th movie was rated by the j-th user
%
% You should set the following variables correctly:
%
% X_grad - num_movies x num_features matrix, containing the
% partial derivatives w.r.t. to each element of X
% Theta_grad - num_users x num_features matrix, containing the
% partial derivatives w.r.t. to each element of Theta
%
predict=(X*Theta') .* R;
J=1/2*sum(sum((predict-Y) .^ 2))+lambda/2*sum(sum(Theta .^ 2))+lambda/2*sum(sum(X .^ 2));
for i=1:num_movies
idx=find(R(i,:)==1);
Thetatemp=Theta(idx,:);
Ytemp=Y(i,idx);
X_grad(i,:)=(X(i,:)*Thetatemp'-Ytemp)*Thetatemp+lambda*X(i,:);
end
for i=1:num_users
idx=find(R(:,i)==1);
Xtemp=X(idx,:);
Ytemp=Y(idx,i);
Theta_grad(i,:)=(Xtemp*Theta(i,:)'-Ytemp)'*Xtemp+lambda*Theta(i,:);
end
% =============================================================
grad = [X_grad(:); Theta_grad(:)];
end