problem with Collect for long polynomial
- To: mathgroup at smc.vnet.net
- Subject: [mg37270] problem with Collect for long polynomial
- From: Troy Goodson <Troy.D.Goodson at jpl.nasa.gov>
- Date: Mon, 21 Oct 2002 02:29:40 -0400 (EDT)
- Organization: JPL/Caltech
- Sender: owner-wri-mathgroup at wolfram.com
I apologize for the length of this post, but I don't see how else to be precise about my question. The short story is this: -- copy and paste the lines below into Mathematica -- execute -- the result is a really big expresssion, but I want the terms in this expression to be grouped in powers of my variable "b". However, Collect doesn't appear to be working right. I call Collect[%, b] and I think I'm getting % back. At the very least, I can clearly see more than one term in the expression that includes b^9, for example. I'd be very grateful if someone a little more knowledgeable than I could execute these lines and see if they can get Collect to work. Of, if this is how Collect is supposed to work, what command should I be using? Thanks, Troy. So, here's what I did. First, to get my equation: denom = Sqrt[(B^2 - r^2)^2 + 4*(r^2)*(b^2)] cnu = (2*b^2 - B^2 + r^2)/denom snu = -2*b*Sqrt[B^2 - b^2]/denom sif = 2*r*b/denom cif = (r^2 - B^2)/denom pdr = -Cos[ds]*Sin[q]*(snu*cif + cnu*sif) - Sin[ds]*(cnu*cif - snu*sif) HH = -(B^2 - b^2)*V^2/(r^2) + (((B*V)^2)/( r^2) - 2*w*b*V*Cos[q]*Cos[ds] + (w* r)^2 - (w*r*pdr)^2)*(Cos[qr])^2 Now, my equation is really HH == 0, but there's some manipulations I want to do first. I don't know Mathematica well, so all I could see to do was to perform operations on HH, then put the equation together. H2 = Expand[HH] H3 = Collect[HH, Sqrt[B^2 - b^2]] H4 = H3*( (4 * (b*r)^2 + (B^2 - r^2)^2)^2 ) H7 = H4*(r^2) H8 = Collect[ Cancel[H7], Sqrt[-b^2 + B^2] ] H9 = Equal[H8, 0] /. Equal[ aa_ + Sqrt[B^2 - b^2]*bb_, 0] -> Equal[ Sqrt[B^2 - b^2]*bb, -aa] H10 = Thread[#^2 &[H9], Equal] // ExpandAll H11 = H10 /. Equal[ mm_ , nn_] -> Equal[ mm - nn , 0] H12 = H10 /. Equal[ qq_ , 0] -> qq For H3 and H8, Collect seems to work. The command to get H10 I copied from a post by Andrzej Kozlowski. H13 = Collect[H11,b] H14 = Collect[H12,b] but the results don't seem to be 'collected' polynomials.