anchor.diff:              
                   mean,cov
               | None ->
  +                let k = k  + Expr.diagMat sigmaNs
                   let kInv        = Expr.invert k
                   let kStar      = covMat x xStar
                   let mean = meanXStar + kStar.T .* kInv .* (y - meanX)
  
positive.code:             let newTauSite = (Expr.loop loopSpec chTauSite [tauSite;vSite;sigma;mu]).[nIters - 1,*]
              let newVSite = (Expr.loop loopSpec chVSite [tauSite;vSite;sigma;mu]).[nIters - 1,*] |> Expr.checkFinite "muSUpd" 
              newTauSite,newVSite
          let tauSite,vSite = optimize 20 (sigma,mu, tauSite,vSite)
          let covSite = (1.0f/tauSite)
          let muSite = (Expr.diagMat covSite) .* vSite
          covSite, muSite
  
negative.code:             match pars with
              | LinPars _ -> linearCovariance z z'
              | SEPars parsSE  -> squaredExpCovariance (parsSE.Lengthscale,parsSE.SignalVariance) z z'
          let k           = (covMat x x)
          let kStarstar  = covMat xStar xStar
          
          let meanFct,monotonicity,cut = 
  