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Re: RowReduce::luc when using NSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99199] Re: RowReduce::luc when using NSolve
  • From: dh <dh at metrohm.com>
  • Date: Wed, 29 Apr 2009 06:40:34 -0400 (EDT)
  • References: <gt6fkm$rru$1@smc.vnet.net>


Hi,

look at the order of magnitude of your coefficients and you will see 

where the problem comes from.

However, why do you want to calculate with approximate numbers (using 

NSolve) if you have an accurate input.

Simply use Solve and you will get an accurate result.

Daniel







mereandor wrote:

> I try to solve a linear equation with the following input to mathematica:

> 

> NSolve[{BesselJ[0, 20] - BesselJ[0, 20] r[0] == 3 I BesselJ[0, 60 I] t[0], BesselJ[0, 20] + BesselJ[0, 20] r[0] == BesselJ[0, 60 I] t[0]}, {r[0], t[0]}]

> 

> but I get

> 

> RowReduce::luc: Result for RowReduce of badly conditioned matrix \

> {{-0.167025+0. I,-1.61061*10^9-<<21>> I,0.167025+0. I},{<<1>>}} may \

> contain significant numerical errors. >>

> 

> This is only the simplest instance of my problem (2(n+1) equations in equally numbered variables). If I don't write the equations down literally but insert them into NSolve as a Table[] statement I don't even get the warning. Then the equations are solved only partially expressing t[n] as linear combination of r[n].

> 

> I use Mathematica 6.0

> 

> How can I resolve this?

> 

> Thanks in advance for any help!

> 




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