# File narray_ext.rb, line 334 def covariance(x,y,*ranks) x = NArray.to_na(x) unless x.kind_of?(NArray) x = x.to_type(NArray::DFLOAT) if x.integer? y = NArray.to_na(y) unless y.kind_of?(NArray) y = y.to_type(NArray::DFLOAT) if y.integer? n = x.rank_total(*ranks) xm = x.accum(*ranks).div!(n) ym = y.accum(*ranks).div!(n) ((x-xm)*(y-ym)).sum(*ranks) / (n-1) end