Re: Almost symbolic computations (?)
- To: mathgroup at smc.vnet.net
- Subject: [mg90505] Re: [mg90466] Almost symbolic computations (?)
- From: DrMajorBob <drmajorbob at att.net>
- Date: Fri, 11 Jul 2008 02:03:25 -0400 (EDT)
- References: <24624830.1215688345875.JavaMail.root@m08>
- Reply-to: drmajorbob at longhorns.com
The tutorial at "VectorAnalysis/tutorial/VectorAnalysis" says, "The initial default coordinate system is Cartesian, with coordinate variables Xx, Yy, and Zz." So you didn't use proper variables. Your specific problem: Curl[{a x, a y, a z}, Cartesian[x, y, z]] {0, 0, 0} should be a special case of Curl[{f[x, y, z], g[x, y, z], h[x, y, z]}, Cartesian[x, y, z]] {-(g^(0,0,1))[x,y,z]+(h^(0,1,0))[x,y,z],(f^(0,0,1))[x,y,z]-(h^(1,0,0))[x,y,z],-(f^(0,1,0))[x,y,z]+(g^(1,0,0))[x,y,z]} A little visual inspection confirms it. Bobby On Thu, 10 Jul 2008 05:35:14 -0500, Barbara Da Vinci <barbaradavinci at tahoo.it> wrote: > Dear MathGroup > > This is an example of the problem > I'm facing. > > The code > > Needs["VectorAnalysis`"]; > Head /@ {ax, ay, az} > A = {ax, ay, az}; > Curl[A] > > returns > > {Symbol, Symbol, Symbol} > {0, 0, 0} > > Instead, I would get the > well known symbolic form > > d_y az - d_z ay > ... > > I have been trying, for > a while, to perform string > manipulations but that, > of course, lays to ashes > the possibility to recognize > > d_y az + d_y az = 2 d_y az > > and so on. > > Any way to get out of it ? > > Kind regards > > > Barbara Da Vinci > > -- DrMajorBob at longhorns.com