ロジスティック回帰におけるトラブル計算コスト

Question

私はCourseraの機械学習でAndrew Ngからコースを受講しています。このassginmentでは、私はMatLabのロジスティック回帰を使ってコスト関数を計算しようとしていますが、 "Error using sfminbx（line 27） 初期ポイントで目的関数が定義されていません。

log（シグモイド（X * theta））が-Infベクトルであるため、以下のcostFunction関数内のコストJがNaNであることを付け加えておきます。私はこれが例外に関連していると確信しています。あなたは助けてもらえますか？

マイコスト関数は次のようになります。

data = load('ex2data1.txt'); 
X = data(:, [1, 2]); y = data(:, 3); 

[m, n] = size(X); 

% Add intercept term to x and X_test 
X = [ones(m, 1) X]; 

% Initialize fitting parameters 
initial_theta = zeros(n + 1, 1); 

% Compute and display initial cost and gradient 
[cost, grad] = costFunction(initial_theta, X, y); 

fprintf('Cost at initial theta (zeros): %f\n', cost); 
fprintf('Expected cost (approx): 0.693\n'); 
fprintf('Gradient at initial theta (zeros): \n'); 
fprintf(' %f \n', grad); 
fprintf('Expected gradients (approx):\n -0.1000\n -12.0092\n -11.2628\n'); 

% Compute and display cost and gradient with non-zero theta 
test_theta = [-24; 0.2; 0.2]; 
[cost, grad] = costFunction(test_theta, X, y); 

fprintf('\nCost at test theta: %f\n', cost); 
fprintf('Expected cost (approx): 0.218\n'); 
fprintf('Gradient at test theta: \n'); 
fprintf(' %f \n', grad); 
fprintf('Expected gradients (approx):\n 0.043\n 2.566\n 2.647\n'); 
fprintf('\nProgram paused. Press enter to continue.\n'); 
pause; 


%% ============= Part 3: Optimizing using fminunc ============= 
% In this exercise, you will use a built-in function (fminunc) to find the 
% optimal parameters theta. 

% Set options for fminunc 
options = optimset('GradObj', 'on', 'MaxIter', 400, 'Algorithm', 'trust- 
region'); 

% Run fminunc to obtain the optimal theta 
% This function will return theta and the cost 

[theta, cost] = ... 
    fminunc(@(t)(costFunction(t, X, y)), initial_theta, options); 

end 

データセットは以下のようになります：この関数を呼び出す

function [J, grad] = costFunction(theta, X, y) 

    m = length(y); % number of training examples 
    J = 0; 
    grad = zeros(size(theta)); 

    h = sigmoid(theta * X); 
    J = - (1/m) * ((log(h)' * y) + (log(1 - h)' * (1 - y))); 
    grad = (1/m) * X' * (h - y); 

end 

私のコードは次のようになります

34.62365962451697、 78.0246928153624,0 30.28671076822607,43.89499752400101,35.84740876993872,72.90219802708364,0 60.18259938620976,86.30855209546826,1 79.0327360507101,75.3443764369103,1 45.08327747668339,56.3163717815305,0 61.10666453684766,96.51142588489624,1 75.02474556738889,46.55401354116538,1 76.09878670226257,87.42056971926803,1 84.43281996120035,43.53339331072109,1 95.86155507093572,38.22527805795094,0 75.01365838958247 、 39.53833914367223,76.03681085115882,0 53.9710521485623,89.20735013750205,1 69.07014406283025,52.74046973016765,1 82.30705337399482,76.48196330235604,1 69.36458875970939,97.71869196188608,1 30.60326323428011,0。 94685547711617,46.67857410673128,0 70.66150955499435,92.92713789364831,1 76.97878372747498,47.57596364975532,1 67.37202754570876,42.83843832029179,0 89.67677575072079,65.79936592745237,1 50.534788289883,48.85581152764205,0 34.21206097786789,44.20952859866288,0 77.9240914545704,68.9​​723599933059,1 62.27101367004632、 69.95445795447587,1 80.1901807509566,44.82162893218353,1 93.114388797442,38.80067033713209,0 61.83020602312595,50.25610789244621,0 38.78580379679423,64.99568095539578,0 61.379289447425,72.80788731317097,1 85.40451939411645,57.05198397627 122,1 52.10797973193984,63.12762376881715,0 52.04540476831827,69.43286012045222,1 40.23689373545111,71.16774802184875,0 54.63510555424817,52.21388588061123,0 33.91550010906887,98.86943574220611,0 64.17698887494485,80.90806058670817,1 74.78925295941542,41.57341522824434,0 34.1836400264419,75.2377203360134、 0 83.90239366249155,56.30804621605327,1 51.54772026906181,46.85629026349976,0 94.44336776917852,65.56892160559052,1 82.36875375713919,40.61825515970618,0 51.04775177128865,45.82270145776001,0 62.22267576120188,52.06099194836679,0 77.19303492601364,70.45820000180959,97.77159928000232,86.7278223300282,62.07306379667647,96。76882412413983,1 91.56497449807442,88.69629254546599,1 79.94481794066932,74.16311935043758,1 99.2725269292572,60.99903099844988,1 90.54671411399852,43.39060180650027,1 34.52451385320009,60.39634245837173,0 50.2864961189907,49.80453881323059,0 49.58667721632031,59.80895099453265,0 97.64563396007767,68.86157272420604、 1 32.57720016809309,95.59854761387875,0 74.24869136721598,69.82457122657193,1 71.79646205863379,78.45356224515052,1 75.3956114656803,85.75993667331619,1 35.28611281526193,47.02051394723416,0 56.25381749711624,39.26147251058019,0 30.05882244669796,49.59297386723685,0 44.66826172480893,66.45008614558913,0 66.56089447242954,41.09209807936973,0 40.45755098375164,97.53518548909936,1 49.07256321908844,51.88321182073966,0 80.27957401466998,92.11606081344084,1 66.74671856944039,60.99139402740988,1 32.72283304060323,43.30717306430063,0 64.0393204150601 、78.03168802018232,1 72.34649422579923,96.22759296761404,1 60.45788573918959,73.09499809758037,1 58.84095621726802,75.85844831279042,1 99.82785779692128,72.36925193383885,1 47.26426910848174,88.47586499559782,1 50.45815980285988,75.80985952982456,1 60.45555629271532,42.50840943572217,0 82.22666157785568,42.71987853716458,0 88.9138964166533,69.80378889835472,1 94.83450672430196,45.69430680250754,1 67.31925746917527,66.58935317747915,1 57.23870631569862,59.51428198012956,1 80.36675600171273,90.96014789746954,1 68.46852178591112 、85.59430710452014,1 42.0754545384731,78.84478600148043,0 75.47770200533905,90.42453899753964,1 78.63542434898018,96.64742716885644,1 52.34800398794107,60.76950525602592,0 94.09433112516793,77.15910509073893,1 90.44855097096364 、87.50879176484702,1 55.48216114069585,35.57070347228866,0 74.49269241843041,84.84513684930135,1 89.84580670720979,45.35828361091658,1 83.48916274498238,48.38028579728175,1 42.2617008099817,87.10385094025457,1 99.31500880510394,68.77540947206617,1 55.34001756003703,64.9319380069486,1 74.77589300092767,89.52981289513276 、1

Answer 1

私が見る唯一の問題は、h = sigmoid(theta * X)の代わりにh = sigmoid(X * theta)と書いたはずです。私は同じ割り当てのために私のコードから取得していたので、これを変更した後にあなたのコードから同じ答えを得ています。