From d79046d7b9677c508df625043f7f5b00d3f1e862 Mon Sep 17 00:00:00 2001
From: Michael Zhang <mail@mzhang.io>
Date: Sun, 8 Oct 2023 01:50:20 -0500
Subject: [PATCH] wtf

---
 gauss_class/gauss_class_2D.m | 40 ++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/gauss_class/gauss_class_2D.m b/gauss_class/gauss_class_2D.m
index cdc8d2c..23bbb31 100644
--- a/gauss_class/gauss_class_2D.m
+++ b/gauss_class/gauss_class_2D.m
@@ -6,6 +6,13 @@ clf;
 prior1 = 0.3;
 prior2 = 0.7;
 
+% mvndis = @(X, mu, Sigma, prior) ( ...
+%     -1/2 * log(2*pi) ...
+%     - log(Sigma) ...
+%     - power(X - mu, 2) / (2 * power(Sigma, 2)) ...
+%     + log(prior) ...
+% );
+
 mu1 = [-1 -1];
 mu2 = [1 1];
 
@@ -30,13 +37,15 @@ mu2 = [1 1];
 
 [X1,X2] = meshgrid(x1,x2);
 %pdf1
-F1 = mvnpdf([X1(:) X2(:)],mu1,Sigma1);
+% F1 = mvnpdf([X1(:) X2(:)],mu1,Sigma1);
+F1 = mvndis([X1(:) X2(:)], mu1, Sigma1, prior1);
 F1 = reshape(prior1 * F1,length(x2),length(x1));
 subplot(1,2,1);
 surf(x1,x2,F1); hold on;
 
 %pdf2
-F2 = mvnpdf([X1(:) X2(:)],mu2,Sigma2);
+% F2 = mvnpdf([X1(:) X2(:)],mu2,Sigma2);
+F2 = mvndis([X1(:) X2(:)], mu2, Sigma2, prior2);
 F2 = reshape(prior2 * F2,length(x2),length(x1));
 surf(x1,x2,F2);
 caxis([min(F2(:))-.5*range(F2(:)),max(F2(:))]);
@@ -54,3 +63,30 @@ subplot(1,2,2);
 imagesc(X1(:),X2(:),cmp);
 
 xlabel('x1'); ylabel('x2');
+
+
+function res = mvndis(X, mu, Sigma, prior)
+    [len, ~] = size(X);
+    res = zeros(len, 1);
+
+    for i = 1:len
+        x = X(i,:);
+        mdist = (x - mu) * inv(Sigma) * (x - mu).';
+        res(i) = -log(2*pi) - 1/2*log(det(Sigma)) - 1/2*mdist + log(prior);
+    end
+    % 1 x 2
+    % (1 x 2) x ((2 x 2) x (2 x 1))
+    % X - mu = 40401 x 2
+    % (40401 x 2) x (2 x 2) x (2 x 40401)
+    % mdist = (X - mu) * inv(Sigma) * (X - mu).';
+    % res = -log(2*pi) - 1/2*log(det(Sigma)) - 1/2*mdist + log(prior)
+    % res = zeros(size(X));
+    % [l1, l2] = size(X);
+    % 
+    % for i1 = 1:l1
+    %     for i2 = 1:l2
+    %         cell = -log(2*pi) - 1/2*log(det(Sigma))
+    %         res(i1, i2) = cell
+    %     end
+    % end
+end