What threshold is plotconfusion applying?
There is some interesting behaviour with plotconfusion when passing it double values instead of categorical values. If I have some predicted responses and plot the confusion matrix like this: plotconfusion(Y', yEst) I get different results from when I do this to set the decision boundary at 0.5 (which is what the confusion() function documentation claims is the boundary used, although I'm not sure if that's what plotconfusion uses). plotconfusion(Y', double(yEst > 0.5)) What is it actually doing behind the scenes?
John Michell answered .
2025-11-20
close all, clear all, clc [ x t ] = cancer_dataset; [ I N ] = size(x) %[ 9 699 ] [ O N ] = size(t) %[ 2 699 ] vart = mean(var(t',1)) % 0.2259 t1 = t(1,:); t2 = t(2,:); N1 = sum(t1), N2 = sum(t2) % 458, 241 m1 = mean(t1), m2 = mean(t2) % 0.6552, 0.3448 vart1 = var(t1,1), vart2 = var(t2,1)% 0.2259, 0.2259 net = patternnet(10); rng(0) [net tr y e ] = train(net,x,t); % y = net(x); e = t - y; NMSE = mse(e)/vart % 0.0984 % NOTE: Although regression error ~ 10%) % classifcation error will only be ~ 3% [c,cm,ind,per] = confusion(t,y) % cm = 446 12 ( 12/458 = 0.0262 ) % 8 233 ( 8/241 = 0.0332 ) % c = 0.0286 ( 20/699 = 0.0286 ) % ( 8/454 = 0.0176 , 12/245 = 0.0490 ) % per = 0.0490 0.0176 0.9824 0.9510 % 0.0176 0.0490 0.9510 0.9824