# need help to resolve accuracy assessment problem

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Natsu dragon il 23 Gen 2018
Commentato: Natsu dragon il 23 Gen 2018
Dear friends im working on unsupervised change detection with kernels on satellite images, since im a beginner in matlab i have a problem about how to calculate the assessment between the result (PreLabel) and ROI (Labels); i found this code
if true switch lower(par);
case {'class'}
Etiquetas = union(Labels,PreLabels); % Class labels (usually, 1,2,3.... but can work with text labels)
NumClases = length(Etiquetas); % Number of classes
% Compute confusion matrix
ConfusionMatrix = zeros(NumClases);
for i=1:NumClases
for j=1:NumClases
ConfusionMatrix(i,j) = length(find(PreLabels==Etiquetas(i) & Labels==Etiquetas(j)));
end;
end;
% Compute Overall Accuracy and Cohen's kappa statistic
n = sum(ConfusionMatrix(:)); % Total number of samples
PA = sum(diag(ConfusionMatrix));
OA = PA/n;
% Estimated Overall Cohen's Kappa (suboptimal implementation)
npj = sum(ConfusionMatrix,1);
nip = sum(ConfusionMatrix,2);
PE = npj*nip;
if (n*PA-PE) == 0 && (n^2-PE) == 0
% Solve indetermination
%warning('0 divided by 0')
Kappa = 1;
else
Kappa = (n*PA-PE)/(n^2-PE);
end
% Cohen's Kappa Variance
theta1 = OA;
theta2 = PE/n^2;
theta3 = (nip'+npj) * diag(ConfusionMatrix) / n^2;
suma4 = 0;
for i=1:NumClases
for j=1:NumClases
suma4 = suma4 + ConfusionMatrix(i,j)*(nip(i) + npj(j))^2;
end;
end;
theta4 = suma4/n^3;
varKappa = ( theta1*(1-theta1)/(1-theta2)^2 + 2*(1-theta1)*(2*theta1*theta2-theta3)/(1-theta2)^3 + (1-theta1)^2*(theta4-4*theta2^2)/(1-theta2)^4 )/n;
Z = Kappa/sqrt(varKappa);
CI = [Kappa + 1.96*sqrt(varKappa), Kappa - 1.96*sqrt(varKappa)];
if NumClases==2
% Wilcoxon test at 95% confidence interval
[p1,h1] = signrank(Labels,PreLabels);
if h1==0
RESULTS.WilcoxonComment = 'The null hypothesis of both distributions come from the same median can be rejected at the 5% level.';
elseif h1==1
RESULTS.WilcoxonComment = 'The null hypothesis of both distributions come from the same median cannot be rejected at the 5% level.';
end;
RESULTS.WilcoxonP = p1;
% Sign-test at 95% confidence interval
[p2,h2] = signtest(Labels,PreLabels);
if h2==0
RESULTS.SignTestComment = 'The null hypothesis of both distributions come from the same median can be rejected at the 5% level.';
elseif h2==1
RESULTS.SignTestComment = 'The null hypothesis of both distributions come from the same median cannot be rejected at the 5% level.';
end;
RESULTS.SignTestP = p2;
% McNemar
RESULTS.Chi2 = (abs(ConfusionMatrix(1,2)-ConfusionMatrix(2,1))-1)^2/(ConfusionMatrix(1,2)+ConfusionMatrix(2,1));
if RESULTS.Chi2<10
RESULTS.Chi2Comments = 'The Chi^2 is not approximated by the chi-square distribution. Instead, the sign test should be used.';
else
RESULTS.Chi2Comments = 'The Chi^2 is approximated by the chi-square distribution. The greater Chi^2, the lower p<0.05 and thus the difference is more statistically significant.';
end
end
% Store results:
RESULTS.ConfusionMatrix = ConfusionMatrix;
RESULTS.Kappa = Kappa;
RESULTS.OA = 100*OA;
RESULTS.varKappa = varKappa;
RESULTS.Z = Z;
RESULTS.CI = CI;
case 'regress'
RESULTS.ME = mean(Labels-PreLabels);
RESULTS.RMSE = sqrt(mean((Labels-PreLabels).^2));
RESULTS.MAE = mean(abs(Labels-PreLabels));
[rr, pp] = corrcoef(Labels,PreLabels);
RESULTS.R = rr(1,2);
RESULTS.RP = pp(1,2);
otherwise disp('Unknown learning paradigm.') end end % code end but i didnt understood lower(par) i always get this error Error in Assessment (line 27) switch lower(par);
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### Risposta accettata

Walter Roberson il 23 Gen 2018
lower() converts a character vector or cell array of character vectors to lowercase. The code is expecting that the variable par contains either 'class' or 'regress' or any upper case version of those including 'CLASS' or 'cLaSS', any combination of upper and lower case whose lowercase equivalent is one of the two.
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Natsu dragon il 23 Gen 2018
thank you for your reply this is what i understood, but i really don't know how to overcome this error

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