Re: Why these graphs differ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg33943] Re: [mg33925] Why these graphs differ?*From*: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>*Date*: Wed, 24 Apr 2002 01:21:52 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Really it is neither. What it really means is that you should study Mathematica a little more. The second Plot is correct while the first is basically nonsense. What you did is make Mathematica try to solve a lot of "differential equations" like this one: DSolve[{Derivative[1][y][4.166666666666666*^-8] == 4.166666666666666*^-8, y[0] == 1}, y[4.166666666666666*^-8], 4.166666666666666*^-8][[1,1, 2]] As you can see yourself this does not make much sense. It is not a bug, just a very basic fact about the way Plot evaluates its arguments. Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/ On Tuesday, April 23, 2002, at 08:13 PM, 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? > > > Vladimir Bondarenko > > > > >