Why do these not work?
- To: mathgroup at smc.vnet.net
- Subject: [mg109697] Why do these not work?
- From: "S. B. Gray" <stevebg at ROADRUNNER.COM>
- Date: Wed, 12 May 2010 07:34:22 -0400 (EDT)
- Reply-to: stevebg at ROADRUNNER.COM
There is something about Mathematica which does not allow the first two calls to
work, and I don't know why. Can anyone give me some guidance?
First, do I need all these things in the Module and is there a shorter
way to "localize" them?
plane3[p1_,p2_,p3_] :=
Module[{x1,y1,z1, x2,y2,z2, x3,y3,z3, iden},
{x1, y1, z1} = p1;
{x2, y2, z2} = p2;
{x3, y3, z3} = p3;
iden = 1/Det[{{x1,y1,z1},{x2,y2,z2},{x3,y3,z3}}];
(* Or 1/Det[{p1,p2,p3}] *)
aa = iden*Det[{{ 1, y1, z1},{ 1, y2, z2},{ 1, y3, z3}}];
bb = iden*Det[{{x1, 1, z1},{x2, 1, z2},{x3, 1, z3}}];
cc = iden*Det[{{x1, y1, 1},{x2, y2, 1},{x3, y3, 1}}];
Return[{aa, bb, cc}]; (* Plane: aa*x + bb*y + cc*z = 1 *)
]
This ReplaceAll gives the numeric answer I want:
plane3[{x1,y1,z1},{x2,y2,z2},{x3,y3,z3}] /.
{x1 -> 1, y1 -> 0, z1 -> 0,
x2 -> 0, y2 -> 1, z2 -> 0,
x3 -> 0, y3 -> 0, z3 -> 1}
{1,1,1}
This ReplaceAll does not work at all:
plane3[q1,q2,q3]/.{q1->{1,0,0},q2->{0,1,0},q3->{0,0,1}}
This ReplaceAll gives a symbolic answer that I do not want:
q1={x1,y1,z1}; q2={x2,y2,z2}; q3={x3,y3,z3};
plane3[q1,q2,q3]/.{q1->{1,0,0},q2->{0,1,0},q3->{0,0,1}}
What is the rule? I note in ReplaceAll x/.{{x->1},{x->3},{x->7}},
but I don't want one at a time.
Thank you for any tips.
Steve Gray