Table 3.

Description of all modeling choices tested with a grid search. See Section 2.4 for explanations of the notation ψ(r) for stationary kernels, the lengthscale parameters λ_j, and the notations of variable decomposition. The piecewise-polynomial kernel of order 2, taken from [35], is defined as such : $\psi (r)={(1-r)}_{+}^{j+2}(1+(j+2)r+\frac{j^2+4j+3}{3}{r}^2)$, where $j=\lfloor \frac{d}{2}+3\rfloor$ and ( ⋅ )₊ = max(⋅, 0) denotes the positive part.

Option	Candidates	Candidates description	Parameters
Mean function	Zero	m(x)=0	None
	Constant	m(x)=c	c
	Linear	m(x)=wTx + c	w, c
	Polynomial	$m(\mathbf{x})=\sum _{i=1}^3{\mathbf{w}}_{\mathbf{i}}^{\mathbf{T}}{\mathbf{x}}^{\mathbf{i}}+c$	wi, c
Kernel function	Squared exponential	$\psi (r)=e^{-\frac{r^2}{2}}$	λi
	Matern 5/2	$\psi (r)=(1+\sqrt{5}r+\frac{5}{3}{r}^2)e^{-\sqrt{5}r}$	λi
	Rational quadratic	$\psi (r)={(1+\frac{r^2}{2\gamma })}^{-\gamma }$	γ, λi
	Piecewise polynomial	See caption	λi
Variable decomposition	None	k = αkBu, Tf, Tm, Cb	α
	Fuel + Mod	k = α kBu, Tf + β kBu, Tm, Cb	α, β
	Bu + Base	k = α kBu + β kBu, Tf, Tm, Cb	α, β
	Tf + Base	k = α kBu, Tf + β kBu, Tf, Tm, Cb	α, β
	Tm + Base	k = α kBu, Tm + β kBu, Tf, Tm, Cb	α, β