# American Institute of Mathematical Sciences

June  2012, 32(6): 2089-2099. doi: 10.3934/dcds.2012.32.2089

## A direct proof of the Tonelli's partial regularity result

Received  April 2011 Revised  July 2011 Published  February 2012

The aim of this work is to give a simple proof of the Tonelli's partial regularity result which states that any absolutely continuous solution to the variational problem $$\min\left\{\int_a^b L(t,u(t),\dot u(t))dt: u\in{\bf W}_0^{1,1}(a,b)\right\}$$ has extended-values continuous derivative if the Lagrangian function $L(t,u,\xi)$ is strictly convex in $\xi$ and Lipschitz continuous in $u$, locally uniformly in $\xi$ (but not in $t$). Our assumption is weaker than the one used in [2, 4, 5, 6, 13] since we do not require the Lipschitz continuity of $L$ in $u$ to be locally uniform in $t$, and it is optimal as shown by the example in [12].
Citation: Alessandro Ferriero. A direct proof of the Tonelli's partial regularity result. Discrete & Continuous Dynamical Systems, 2012, 32 (6) : 2089-2099. doi: 10.3934/dcds.2012.32.2089
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