For the number of complete shock curves of a conservation law with one space variable,Hopf in 1950 for the Burger equation,and Oleinik in 1956 for the general,stated that it is at most countable.In 1979,the present author published an example to show that the statement of Hopf and Oleinik is wrong.But after so long time,the wrong statement for countability still appeared in some publications,which is at least partly due to that some ones felt difficult to understand Hopf and Oleinik’s proofs being wrong.So,pointing out where they went wrong becomes very necessary.
LI BangHe Academy of Mathematics and Systems Science,Chinese Academy of Sciences,Beijing 100190,China
For a conservation law with convex condition and initial data in L∞(R), it had been commonly believed that the number of discontinuity lines (or shock waves) of the solution is at most countable since Theorem 1 in Oleinik's seminal paper published in 1956 asserted this fact. In 1977, the author gave an example to show that there is an initial data in C∞(R) ∩ L∞(R) such that the number of shock waves is uncountable. And in 1980, he gave an example to show that there is an initial data in C(R)∩L∞(R) such that the measure of original points of shock waves on the real axis is positive. In this paper, he proves further that the set consisting of initial data in C(R) ∩ L∞(R) with the property: almost all points on the real axis are original points of shock waves, is dense in C(R) ∩ L∞(R). All these results show that Oleinik's assertion on the countability of discontinuity lines is wrong.
