Re: Why these graphs differ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg33942] Re: Why these graphs differ?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Wed, 24 Apr 2002 01:21:50 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <aa3gm6$80q$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Vladimir Bondarenko wrote: > > These solutions, naturally, coincide. > > DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]] > Evaluate[DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]]] > > (2 + z^2)/2 > (2 + z^2)/2 > > But, surprisingly, the corresponding graphs are not identical: > > Plot[ DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]], {z, 0, 1}] > Plot[Evaluate[DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]]], {z, 0, 1}] > > Is it a feature or a problem? The Part[expr,1,1,2] is z for expr:> DSolve[{y'[z] == z, y[0] == 1}, y[z], z] and the Part[expr,1,1,2] is (2+z^2)/2 for expr:> {{y[z] -> (2 + z^2)/2}} so there is no wonder, that the results are differnt. Different expressions may have also different parts. Regards Jens