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...
>
>

```

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