diff DL/two-step DL/dico_decorr.m @ 152:485747bf39e0 ivand_dev

Two step dictonary learning - Integration of the code for dictionary update and dictionary decorrelation from Boris Mailhe

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DL/two-step DL/dico_decorr.m	Thu Jul 28 15:49:32 2011 +0100
@@ -0,0 +1,48 @@
+function dico = dico_decorr(dico, mu, amp)
+    %DICO_DECORR decorrelate a dictionary
+    %   Parameters:
+    %   dico: the dictionary
+    %   mu: the coherence threshold
+    %   amp: the amplitude coefficients, only used to decide which atom to
+    %   project
+    %
+    %   Result:
+    %   dico: a dictionary close to the input one with coherence mu.
+    
+    % compute atom weights
+    if nargin > 2
+        rank = sum(amp.*amp, 2);
+    else
+        rank = randperm(length(dico));
+    end
+    
+    % several decorrelation iterations might be needed to reach global
+    % coherence mu. niter can be adjusted to needs.
+    niter = 1;
+    while niter < 5 && ...
+            max(max(abs(dico'*dico -eye(length(dico))))) > mu + 10^-6
+        % find pairs of high correlation atoms
+        colors = dico_color(dico, mu);
+        
+        % iterate on all pairs
+        nbColors = max(colors);
+        for c = 1:nbColors
+            index = find(colors==c);
+            if numel(index) == 2
+                % decide which atom to change (the one with lowest weight)
+                if rank(index(1)) < rank(index(2))
+                    index = fliplr(index);
+                end
+                
+                % update the atom
+                corr = dico(:,index(1))'*dico(:,index(2));
+                alpha = sqrt((1-mu*mu)/(1-corr*corr));
+                beta = corr*alpha-mu*sign(corr);
+                dico(:,index(2)) = alpha*dico(:,index(2))...
+                    -beta*dico(:,index(1));
+            end
+        end
+        niter = niter+1;
+    end
+end
+