diff options
Diffstat (limited to 'sourcecodes/bnt-master/KPMstats/gaussian_prob.m')
| -rw-r--r-- | sourcecodes/bnt-master/KPMstats/gaussian_prob.m | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/sourcecodes/bnt-master/KPMstats/gaussian_prob.m b/sourcecodes/bnt-master/KPMstats/gaussian_prob.m new file mode 100644 index 00000000..0ac0b765 --- /dev/null +++ b/sourcecodes/bnt-master/KPMstats/gaussian_prob.m @@ -0,0 +1,28 @@ +function p = gaussian_prob(x, m, C, use_log) +% GAUSSIAN_PROB Evaluate a multivariate Gaussian density. +% p = gaussian_prob(X, m, C) +% p(i) = N(X(:,i), m, C) where C = covariance matrix and each COLUMN of x is a datavector + +% p = gaussian_prob(X, m, C, 1) returns log N(X(:,i), m, C) (to prevents underflow). +% +% If X has size dxN, then p has size Nx1, where N = number of examples + +if nargin < 4, use_log = 0; end + +if length(m)==1 % scalar + x = x(:)'; +end +[d N] = size(x); +%assert(length(m)==d); % slow +m = m(:); +M = m*ones(1,N); % replicate the mean across columns +denom = (2*pi)^(d/2)*sqrt(abs(det(C))); +mahal = sum(((x-M)'*inv(C)).*(x-M)',2); % Chris Bregler's trick +if any(mahal<0) + warning('mahal < 0 => C is not psd') +end +if use_log + p = -0.5*mahal - log(denom); +else + p = exp(-0.5*mahal) / (denom+eps); +end |
