Re: Why do these not work?

*To*: mathgroup at smc.vnet.net*Subject*: [mg109719] Re: Why do these not work?*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Thu, 13 May 2010 07:25:32 -0400 (EDT)

---- "S. B. Gray" <stevebg at ROADRUNNER.COM> wrote: ============= 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 -- Bob Hanlon