# zbMATH — the first resource for mathematics

A variational calculus for discontinuous solutions of systems of conservation laws. (English) Zbl 0846.35080
The paper is concerned with the Cauchy problem for the perturbed system of conservation laws in a single variable: $u_t+ [F(u)]_x= h(t, x, u),\quad u(0, x)= \overline u(x),$ where $$F: \mathbb{R}^n\to \mathbb{R}^n$$ and $$h: [0, \infty)\times \mathbb{R}\times \mathbb{R}^n\to \mathbb{R}^n$$ are smooth functions. It is assumed that the system is strictly hyperbolic, and each characteristic field is either linearly degenerate or genuinely nonlinear in the sense of Lax. For initial conditions $$u(0, x)= \overline u^\varepsilon(x)$$ depending on a small parameter $$\varepsilon$$, the behavior of first-order variation of solutions $$u^\varepsilon(t, x)$$ is studied when the solutions $$u^\varepsilon$$ contain shocks, namely, discontinuities. Introducing “generalized tangent vectors” to solutions, consisting of measures whose absolutely continuous part is some $$L^1$$ function and whose singular part is given by point charges, and then determining their evolution in time, the authors provide a description of corresponding solutions $$u^\varepsilon (t, \cdot)$$ with first-order accuracy w.r.t. $$\varepsilon$$ under suitable regularity assumptions and show that the perturbed solutions $$u^\varepsilon(t, \cdot)$$ still admit a first-order approximation even after the interaction of two shocks of $$u^\varepsilon$$.