Re: Solving equations and inequalities with Reduce - how?
- To: mathgroup at smc.vnet.net
- Subject: [mg87692] Re: Solving equations and inequalities with Reduce - how?
- From: dh <dh at metrohm.ch>
- Date: Tue, 15 Apr 2008 06:50:32 -0400 (EDT)
- References: <fu1tuf$ogc$1@smc.vnet.net>
Hi Marc,
your syntax is correct. But you met a common pit fall. On of your
variables already had a value (of 1) and therefore got replaced by this
value before Reduce got it. You may clear a value by e.g. a=. or Clear[a].
hope this helps, Daniel
Marc Heusser wrote:
> I tried to solve equations with Reduce and somehow did not quite
> formulate it right, so Reduce complains with
> "Reduce::ivar: 1 is not a valid variable".
>
> This is what I tried:
>
> Wanted: A six digit number satisfying the following conditions:
> The first digit is not zero.
> If you take the first two digits and move them to the end of the number,
> the resulting number must be twice the original number.
>
> In[23]:=Reduce[200000a +20000 b +2000 c+200 d+20 e + 2 f
> \[Equal]100000c +10000 d +1000 e+100 f+10 a + b , {a,b,c,d,e,f},
> Modulus\[Rule]9]
>
> I did solve the problem through exhaustive search:
>
> In[14]:=Timing[Select[Range[10^6], FractionalPart[#/10000] 1000000 +
> IntegerPart[#/10000]\[Equal] 2 #&]]
> Out[14]={34.2848 Second,{142857,285714,428571}}
>
> but would like to understand how to use Reduce (or another function) to
> solve such a set of equations.
>
> TIA
>
> Marc
>