quasilinear hyperbolic system; precise formula; critical time; shock wave; transformation; Riemann invariants; isentropic non-viscous compressible fluid flow
In this paper the exact formula for the critical time of generating discontinuity (shock wave) in a solution of a $2\times2$ quasilinear hyperbolic system is derived. The applicability of the formula in the engineering praxis is shown on one-dimensional equations of isentropic non-viscous compressible fluid flow.
 A. D. Myškis A. M. Filimonov: Continuous solutions of quasi-linear hyperbolic systems with two independent variables. (Russian). Differenciaľnyje uravnenija XVII (1981), 488 - 500.
 I. Straškraba V. Jezdinský: Critical times of generating shocks on smooth one-dimensional pressure wakes in inviscid fluids
. Acta Technica 28 (1983), No. 5, 629-642. MR 0727520