comparison toolboxes/FullBNT-1.0.7/KPMstats/linear_regression.m @ 0:e9a9cd732c1e tip

first hg version after svn

+function [muY, SigmaY, weightsY]  = linear_regression(X, Y, varargin)
+% LINEAR_REGRESSION Fit params for P(Y|X) = N(Y;  W X + mu, Sigma) 
+%
+% X(:, t) is the t'th input example
+% Y(:, t) is the t'th output example
+%
+% Kevin Murphy, August 2003
+%
+% This is a special case of cwr_em with 1 cluster.
+% You can also think of it as a front end to clg_Mstep.
+
+[cov_typeY, clamp_weights,  muY, SigmaY, weightsY,...
+ cov_priorY,  regress, clamp_covY] = process_options(...
+    varargin, ...
+     'cov_typeY', 'full', 'clamp_weights', 0, ...
+     'muY', [], 'SigmaY', [], 'weightsY', [], ...
+     'cov_priorY', [], 'regress', 1,  'clamp_covY', 0);
+     
+[nx N] = size(X);
+[ny N2] = size(Y);
+if N ~= N2
+  error(sprintf('nsamples X (%d) ~= nsamples Y (%d)', N, N2));
+end
+
+w = 1/N;
+WYbig = Y*w;
+WYY = WYbig * Y'; 
+WY = sum(WYbig, 2);
+WYTY = sum(diag(WYbig' * Y));
+if ~regress
+  % This is just fitting an unconditional Gaussian
+  weightsY = [];
+  [muY, SigmaY] = ...
+      mixgauss_Mstep(1, WY, WYY, WYTY, ...
+		     'cov_type', cov_typeY, 'cov_prior', cov_priorY);
+  % There is a much easier way...
+  assert(approxeq(muY, mean(Y')))
+  assert(approxeq(SigmaY, cov(Y') + 0.01*eye(ny)))
+else
+  % This is just linear regression
+  WXbig = X*w;
+  WXX = WXbig * X';
+  WX = sum(WXbig, 2);
+  WXTX = sum(diag(WXbig' * X));
+  WXY = WXbig * Y';
+  [muY, SigmaY, weightsY] = ...
+      clg_Mstep(1, WY, WYY, WYTY, WX, WXX, WXY, ...
+		'cov_type', cov_typeY, 'cov_prior', cov_priorY);
+end
+if clamp_covY, SigmaY = SigmaY; end
+if clamp_weights,  weightsY = weightsY; end
+
+if nx==1 & ny==1 & regress
+  P = polyfit(X,Y); % Y = P(1) X^1 + P(2) X^0 = ax + b
+  assert(approxeq(muY, P(2)))
+  assert(approxeq(weightsY, P(1)))
+end
+
+%%%%%%%% Test
+if 0 
+  c1 = randn(2,100);   c2 = randn(2,100);
+  y = c2(1,:); X = [ones(size(c1,2),1) c1'];
+  b = regress(y(:), X); % stats toolbox
+  [m,s,w] = linear_regression(c1, y);
+  assert(approxeq(b(1),m))
+  assert(approxeq(b(2), w(1)))
+  assert(approxeq(b(3), w(2)))
+end