Support for harmmean operator

@sdpvar/harmmean.m

@@ -0,0 +1,55 @@
+function varargout = harmmean(varargin)
+%GEOMEAN (overloaded)
+%
+% t = HARMMEAN(X)
+% For real vector X, returns length(X)/sum(X.^-1))
+
+% See also SDPVAR, GEOMEAN
+
+switch class(varargin{1})
+
+    case 'sdpvar' % Overloaded operator for SDPVAR objects. Pass on args and save them.
+
+        if nargin == 2 && isequal(varargin{2},2)
+            varargout{1} = harmmean(varargin{1}')';
+            return
+        end
+
+        X = varargin{1};
+        [n,m] = size(X);
+        if is(varargin{1},'hermitian') | min(n,m)==1
+            varargout{1} = yalmip('define',mfilename,varargin{:});
+        else
+            % Create one variable for each column
+            y = [];
+            for i = 1:m
+                index = (1+n*(i-1)):i*n;
+                x = extsubsref(X,index);
+                y = [y yalmip('define',mfilename,x)];
+            end
+            varargout{1} = y;
+        end
+
+    case 'char' % YALMIP send 'model' when it wants the epigraph or hypograph
+        if isequal(varargin{1},'graph')
+            t = varargin{2}; % Second arg is the extended operator variable
+            X = varargin{3}; % Third arg and above are the args user used when defining t.
+
+            n = length(X);
+            z = sdpvar(n,1);          
+
+            F = [X >= 0, sum(z) <= n*t];
+            F = [F, cone([(X+z)';(X-z)';2*repmat(t,1,n)])];
+
+            varargout{1} = F;
+            varargout{2} = struct('convexity','concave','monotonicity','increasing','definiteness','positive');          
+            varargout{3} = X;
+        else
+
+            varargout{1} = [];
+            varargout{2} = [];
+            varargout{3} = [];
+
+        end
+    otherwise
+end