Re: RowReduce::luc when using NSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg99159] Re: [mg99135] RowReduce::luc when using NSolve*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Wed, 29 Apr 2009 03:47:49 -0400 (EDT)*Reply-to*: hanlonr at cox.net

As stated in the documentation, NSolve is intended to give a list of numerical approximations to the roots of a polynomial equation. I suggest that you use FindRoot eqn = { 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]}; FindRoot[eqn, {{r[0], 5}, {t[0], 3}}, WorkingPrecision -> 30] {r[0] -> -0.8000000000000000000000000000000000000000000000000000000301`30. - 0.6000000000000000000000000000000000000000000000000000000222`30.*I, t[0] -> 5.66754261149722224656310043127626802663146216598467`30.*^-27 - 1.700262783449166673968930129382880407989438649795398`30.*^-26.\ 700262783449166673968930129382880407989438649795398`30.**I} soln = FindRoot[eqn, {{r[0], -0.8 - 0.6 I}, {t[0], 0}}] {r(0)->-0.8-0.6 I,t(0)->5.66754*10^-27-1.70026*10^-26 I} eqn /. soln {True,True} Bob Hanlon ---- mereandor <mereandor at gmail.com> 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!