What's the reproducing kernel of $H^1(a,b)$?

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I would have thought to find this question here on MSE, but I couldn't find it. I know from https://en.wikipedia.org/wiki/Reproducing_kernel_Hilbert_space#Common_examples that the Laplacian kernel is the reproducing kernel of $H^1(\mathbb R)$ (why is there no $\sigma$ in the norm, btw?), but I couldn't find any reference for a compact interval $[a,b]$. Can anybody help me out?

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The kernel is: $$ K(x,y)= \begin{cases} \sigma\frac{\cosh(\sigma(x - b))\cosh(\sigma (t - a))}{\sinh(\sigma(b-a))}\text{ for }a\leq t\leq x\leq b\\ \sigma\frac{\cosh(\sigma(x - a))\cosh(\sigma(t - b))}{\sinh(\sigma(b-a))}\text{ for }a\leq x\leq t\leq b.\\ \end{cases}$$ This can be checked by direct verification of the reproducing property using integration by parts from the definition of the inner product $\langle f,g \rangle=\int_a^bf(u)g(u)\,du + \frac 1 {\sigma^2}\int_a^bf'(u)g'(u)\,du$.

Complete derivation with $\sigma=1$ can be found in Section 2.11 of the script by Schaback or in Chapter 6 Section 1.6.1 of Berlinet/Thomas-Agnan.