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Short helpfile for action COVARIANCE_MATRIX
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The following arguments are compulsory: 

                WEIGHTS - this keyword takes the label of an action that calculates a 
                          vector of values. The elements of this vector are used as weights 
                          for the input data points. 

In addition you may use the following options: 

            UNORMALIZED - ( default=off ) do not divide by the sum of the weights 
                    ARG - the vectors of data from which we are calculating the 
                          covariance. You can use multiple instances of this keyword i.e. ARG1, 
                          ARG2, ARG3... 


