Re: Solve problem
- To: mathgroup at smc.vnet.net
- Subject: [mg98036] Re: Solve problem
- From: "m.g." <mg at michaelgamer.de>
- Date: Sat, 28 Mar 2009 05:44:47 -0500 (EST)
- References: <gqia5h$oj3$1@smc.vnet.net>
On 27 Mrz., 11:35, araldocampan... at gmail.com wrote:
> I have a Solve[...] which gives me solutions like
> {{b1 -> -2, a1 -> -1 }, {b1 -> 0.5, a1 -> 3}}
> or like
> {{a1 -> 1, b1 -> 3}}
>
> How can I get the positive value for a1, which is 3
> in the first case and 1 in the second one?
>
> Bruno
Hello Bruno,
maybe you think of the following:
A system of equations - yust as it came in my mind :-)
In[42]:= gls={2 x+3 y==2,7 x-5 y^2==3}
Out[42]= {2 x+3 y==2,7 x-5 y^2==3}
the solution
In[43]:= lsg=Solve[gls,{x,y}] // N
Out[43]= {{x->0.506033,y->0.329311}, {x->4.64397,y->-2.42931}}
extracting values
In[45]:= temp={x,y} /. lsg
Out[45]= {{0.506033,0.329311},{4.64397,-2.42931}}
Selecting positive solution:
In[49]:= Select[temp,#[[2]]>0&]
Out[49]= {{0.506033,0.329311}}
Greetings
Mike