Re: Thread::tdlen: Objects of unequal length

*To*: mathgroup at smc.vnet.net*Subject*: [mg121908] Re: Thread::tdlen: Objects of unequal length*From*: Vivek Joshi <vivekjjoshi29 at gmail.com>*Date*: Thu, 6 Oct 2011 04:23:30 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201110050804.EAA07154@smc.vnet.net>

Times is just an element wise multiplication. Are you trying to do a dot product ? s = {{x1, x2, x3, x4}}; t = {{0.0284435, 0.00395759, 0.000211963, 0.0357403}, {0.00395759, 0.0113862, -0.000199939, -0.000556137}, {0.000211963, -0.000199939, 0.00118147, -0.00043913}, {0.0357403, -0.000556137, -0.00043913, 0.0649449}}; Dot[Dot[s, t], Transpose[s]] // Simplify {{0.0284435 x1^2 + 0.0113862 x2^2 - 0.000399878 x2 x3 + 0.00118147 x3^2 + x1 (0.00791518 x2 + 0.000423926 x3 + 0.0714806 x4) - 0.00111227 x2 x4 - 0.00087826 x3 x4 + 0.0649449 x4^2}} Vivek On Wed, Oct 5, 2011 at 4:04 AM, SysInv <johan at systeminvestors.se> wrote: > This problem is driving me crazy. I'm trying to multiply matrices, where > one is 1x4 (s) and the other is 4x4 (t) and the multiplication is > s*t*Transpose[s] > > Despite this I get the error message that the objects is of unequal length. > The matrices are: > > s={{x1,x2,x3,x4}} > > > t={0.0284435,0.00395759,0.000211963,0.0357403},{0.00395759,0.0113862,-0.000199939,-0.000556137},{0.000211963,-0.000199939,0.00118147,-0.00043913},{ > 0.0357403,-0.000556137,-0.00043913,0.0649449} > > I must use double level in the 1 row matrix, since otherwise Transpose[] > complains that it needs at least 2 levels. I tried without this as well, but > I keep getting: > > Thread::tdlen : Objects of unequal length in > {{x1,x2,x3,x4}}{{0.0284435,0.00395759,0.000211963,0.0357403},<<2>>,{<<10>>,<<3>>}}{{x1},{x2},{x3},{x4}} > cannot be combined. >> > > . when I run s*t*Transpose[s]. > > I've spent hours trying to figure this simple problem out, but without any > luck. Any pointers guys? It doesn't help if I change the order of the > transpose... > >

**References**:**Thread::tdlen: Objects of unequal length***From:*SysInv <johan@systeminvestors.se>