anchor.diff:              let inp_mean_val = inp_meanhost |> post device
   
               let inp_covhost =  rand.UniformArrayND (0.0f ,2.0f) [1;ngps;ngps]
  -            let inp_covhost = makePsd inp_covhost
  +            let inp_covhost = fPsd inp_covhost
               let inp_cov_val = inp_covhost |> post device
  -
  -
  -        let pred_mean, pred_cov = pred_mean_cov_fn inp_mean_val inp_cov_val
  -
  +            
  +            
  +            let pred_mean, pred_cov = pred_mean_cov_fn inp_mean_val inp_cov_val
  +            
               let testInOut = {
                   In_Mean = inp_meanhost;
                   In_Cov = inp_covhost;
                   Pred_Mean = pred_mean;
                   Pred_Cov = pred_cov}
   
  -        printfn "Lengthscales=\n%A" mi.ParameterStorage.[!mgp.Lengthscales]
  -        printfn "TrnX=\n%A" mi.ParameterStorage.[!mgp.TrnX]
  -        printfn "TrnT=\n%A" mi.ParameterStorage.[!mgp.TrnT]
  -        printfn "TrnSigma=\n%A" mi.ParameterStorage.[!mgp.TrnSigma]
  -        printfn ""
  -        printfn "inp_mean=\n%A" inp_mean_val
  -        printfn "inp_cov=\n%A" inp_cov_val
  -        printfn ""
  -        printfn "pred_mean=\n%A" pred_mean
  -        printfn "pred_cov=\n%A" pred_cov
  +            printfn "Lengthscales=\n%A" mi.ParameterStorage.[!mgp.Lengthscales]
  +            printfn "TrnX=\n%A" mi.ParameterStorage.[!mgp.TrnX]
  +            printfn "TrnT=\n%A" mi.ParameterStorage.[!mgp.TrnT]
  +            printfn "TrnSigma=\n%A" mi.ParameterStorage.[!mgp.TrnSigma]
  +            printfn ""
  +            printfn "inp_mean=\n%A" inp_mean_val
  +            printfn "inp_cov=\n%A" inp_cov_val
  +            printfn ""
  +            printfn "pred_mean=\n%A" pred_mean
  +            printfn "pred_cov=\n%A" pred_cov
   
               testInOut
           
  
positive.code:         let ntraining = 10
          let ntest = 10
  
          let m: ExprT<single> = Expr.var "m" [SizeSpec.symbol "nTstSmpls";SizeSpec.symbol "nGPs"; SizeSpec.symbol "nGPs"]
          let psd = m.* m
          let cmplr = DevHost.Compiler, CompileEnv.empty
          let makePsd = Func.make cmplr psd |> arg1 m
  
          let mb = ModelBuilder<single> "Test"
  
  
negative.code: 
      let testMultiGPLayer device =
  
          
          let seed = 1
          let rand = Random(seed)
  
  