Re: DSolve bug
- To: mathgroup at smc.vnet.net
- Subject: [mg97819] Re: [mg97768] DSolve bug
- From: Sotirios Bonanos <sbonano at inp.demokritos.gr>
- Date: Sun, 22 Mar 2009 05:50:29 -0500 (EST)
Your example gives two different ways of referring to the same function (Sin[a*x]). But I want to be able to use the arbitrary function in the solution given by DSolve (and its derivatives) in other expressions. This I cannot do because the derivatives D[f1[x][y], x, y], D[f1[x][y], y, x] are not equal: Clear[f1, f2] {D[f1[x][y], x, y], D[f1[x][y], y, x]} That's why I claim, if it is not a bug, it is an unfortunate choice of representation! Sotirios Bonanos ----- "Bob Hanlon" wrote: > It is just an alternate representation > > Clear[f1, f2] > > f1[a_][x_] := Sin[a*x] > > f2[a_, x_] := Sin[a*x] > > f1[c][t] == f2[c, t] > > True > > {Plot3D[f1[a][x], {x, 0, 2 Pi}, {a, 1, 3}], > Plot3D[f2[a, x], {x, 0, 2 Pi}, {a, 1, 3}]} > > Some people prefer the f[a][x] representation to explicitly separate out > parameter(s) from argument(s) > > If you prefer > > DSolve[D[F[x, y, z], x, y] == 0, F[x, y, z], {x, y, z}] > > {{F(x,y,z)->Subscript[c, 1][z][x]+Subscript[c, 2][z][y]}} > > % /. f_[arg1_][arg2_] :> f[arg2, arg1] > > {{F(x,y,z)->Subscript[c, 1][x,z]+Subscript[c, 2][y,z]}} > > > > Bob Hanlon > > > On Sat, Mar 21, 2009 at 10:25 AM , Sotirios Bonanos wrote: > > > Hello, > > I have encountered the following bug in DSolve: > > DSolve[D[F[x, y, z], x, y] == 0, F[x, y, z], {x, y, z}] > > gives {{F[x, y, z] -> C[1][z][x] + C[2][z][y]}} > > instead of {{F[x, y, z] -> C[1][x, z] + C[2][y, z]}} > > I don't know if this has been fixed in Mathematica 7, but it is > > present in versions 5 and 6. > > S. Bonanos http://www.inp.demokritos.gr/~sbonano/ >