how to do isolines with 3 data series

Hi, i am trying to do a 2-d isoline plot where i have x values, y values and its corresponding performance e.g. RMSE (root mean squared error). I know that using countourf i need to have x,y,z but i am not sure how to create z using my RMSE values.

X Y RMSE

0.29288454 2.33445535 0.11288079

0.06553189 3.19037484 0.14241216

0.22772855 2.67067976 0.1285208

0.16724828 2.75664266 0.13069577

0.01096461 2.86919603 0.12996041

thanks!

[Mohammad Abouali]

If you want isolines of the same RMSE, then RMSE is your Z

[sensation]

Z must be at least 2x2 matrix but in my case is 1x1...