Let $K:X \times X \to \mathbb R$ be a (positive-definite) kernel and let $H$ be the induced *reproducing kernel Hilbert space (RKHS)*. Fix $(x_1,y_1),\ldots,(x_n,y_n) \in X \times \mathbb R$. For $t \ge 0$, consider the functional $L:H \to \mathbb R$ defined by

$$ \tag{1} L(h) := \sum_{i=1}^n (|h(x_i)-y_i|+t\|h\|)^2. $$

Question.Is there a representer theorem for minimizers of $L$? That is, is it true that every minimizer $h$ of $L$ can be written as $h = \sum_{i=1}^n c_i K_{x_i}$, where the $c_i$'s are scalars and $K_{x_i} \in H$ is defined by $K_{x_i}(x) = K(x_i,x)$ for any $x \in X$?

Note that if $t=0$, then $L = \sum_{i=1}^n (h(x_i)-y_i)^2$, and the classical representer theorem applies.

More generally, given functions $G:\mathbb R^{n+1} \to \mathbb R$ and $u:\mathbb R \to \mathbb R$, I'm interested in conditions under which the functional $L:H \to \mathbb R$ defined by $$ L(h) := G(u(x_1,y_1),\ldots,u(x_n,y_n),\|h\|), $$ admits a representer theorem. In particular, (1) corresponds to the case where $G(r_1,\ldots,r_n,b) = \sum_i^n (r_i + t b)^2$ and $u(c,d) = |c-d|$, for all $r_1,\ldots,r_n,b,c,d \in \mathbb R$.

## A perhaps useful observation

For any $\alpha \in (0,1)$, define the function $L_{\alpha}:H \to \mathbb R$ by $$ L_{\alpha}(h) := \dfrac{1}{\alpha}\sum_{i=1}^n(h(x_i)-y_i)^2 + \dfrac{t^2}{1-\alpha}\|h\|^2. $$

Then, for the function $L:H \to \mathbb R$ defined in (1), one has the identity

$$ L(h) = \inf_{\alpha \in (0,1)}L_{\alpha}(h). $$

It is clear that the $L_{\alpha}$'s admit a representer theorem. I don't know if any of this is useful.