Nguyen-9: sin(x) + sin(y^2) from 100 points in [-1, 1]^2
8 islands of 500 trees, until the RMSE is at most 5.78e-11

Target after 7 generations and 25727 evaluations
RMSE on the 100 training points: 0.00e0
RMSE on the 500 test points:     0.00e0

the expression, 7 nodes of depth 3:
add(sin(mul(y, y)), sin(x))
