NAME:
  pdf2covar
 PURPOSE:   (one line only)
  Convert a probability density function to a covariance matrix
 DESCRIPTION:
 CATEGORY:
  Statistics
 CALLING SEQUENCE:
  pdf2cover,pdf,covar
 INPUTS:
  pdf - Probability density function, this is an NxM array where M is 
          the number of samples in the PDF and N is the number of variables.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  covar - Covariance matrix, this is an NxN matrix
 KEYWORD OUTPUT PARAMETERS:
  MEANS - the mean value of each variable computed from the pdf
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2018/02/01, Written by Marc W. Buie, Southwest Research Institute