       Re: Thread function now working as expected

• To: mathgroup at smc.vnet.net
• Subject: [mg74607] Re: Thread function now working as expected
• From: Peter Pein <petsie at dordos.net>
• Date: Wed, 28 Mar 2007 01:40:52 -0500 (EST)
• References: <euan64\$do9\$1@smc.vnet.net>

```siewsk at bp.com schrieb:
> I cannot get the Thread function to work on In and I
> am forced to do it manually in In
>
> Does anyone has any idea why In is not working as I expected?
>
> In:= eqn1 = Sqrt[1 + 196*x^4] == 12*x - 1 - 14*x^2
> Out=
>               4                     2
> Sqrt[1 + 196 x ] == -1 + 12 x - 14 x
>
>
> In:= eqn2 = Thread[(#1^2 & )[eqn1], Equal]
> Out=
>          4                     2 2
> 1 + 196 x  == (-1 + 12 x - 14 x )
>
>
> In:= dummy = Thread[Expand[eqn2], Equal]
> Out=
>          4                     2 2
> 1 + 196 x  == (-1 + 12 x - 14 x )
>
>
> In:= eqn3 = Equal[ eqn2[] , Expand[ eqn2[] ]  ]
> Out=
>          4                    2        3        4
> 1 + 196 x  == 1 - 24 x + 172 x  - 336 x  + 196 x
>
>
> In:= Simplify[eqn3]
> Out=
>                   2
> x (6 - 43 x + 84 x ) == 0
>
>

Hi,

I guess, Expand evaluates before Mathematica "sees" the Thread, because
In:=
Out=
1 + 196*x^4 == 1 - 24*x + 172*x^2 - 336*x^3 + 196*x^4

evaluates to the desired result.

In:= Simplify[eqn3]
Out= x*(6 - 43*x + 84*x^2) == 0

But because I'm too lazy to type all these Thread[...,Equal], I would prefer

In:= Simplify[(#1^2 & ) /@ eqn1]
Out= x*(6 - 43*x + 84*x^2) == 0

Peter

```

• Prev by Date: Re: Thread function now working as expected
• Next by Date: Re: Cantor Function problem