> Date: Thu, 25 Feb 1999 17:28:39 -0500 > From: Victor Albis <email@example.com> > To: firstname.lastname@example.org > Subject: [HM] Variation/Parameter
> Dear Coleagues, > > Does any of you know who introduced the variation of parameters method > in DE? > I do not know too much about DE, but somebody asked the above question, > and I would like to answer it as accurate as possible. >
An interesting question. See my note on the matter in
Int. J. Math. Educ. Sci. Tech. 14 (1983), pp 789-791.
Briefly the answer is "Cauchy", but there are anticipations by Euler, that weren't available 10 years ago. It may be that the Euler project has made them available in the meantime. I'll ask my colleague Hans Lausch, who is involved with it.
It is usual (but wrong) to attribute the technique to Lagrange.
Kreyszig's well-known text did. In the 7th edition the attribution has altered (somewhat) following a letter I wrote to Kreyszig.