Re: NullSpace[m], why different result for symbolic vs numerical matrix?
- To: mathgroup at smc.vnet.net
- Subject: [mg59232] Re: NullSpace[m], why different result for symbolic vs numerical matrix?
- From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
- Date: Wed, 3 Aug 2005 01:19:39 -0400 (EDT)
- Organization: Uni Leipzig
- References: <dcmu9h$gjd$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi, the nullspace is not unique defined. Any linear combination of the vectors that span the null space will do it. The symbolic and the numeric version use different algorithms and so get different results. Regards Jens "Nasser Abbasi" <nma at 12000.org> schrieb im Newsbeitrag news:dcmu9h$gjd$1 at smc.vnet.net... | | hello, This 5.2 on windows. | | The help for NullSpace function says: | | "NullSpace works on both numerical and symbolic matrices. " | | But why do I get different answer if matrix A is numeric vs symbolic? | | What Am I missing? | | Both answers are correct in the sense that A times each of null | vectors produced does give 0. | | ------------ | Remove["Global`*"] | A = {{0, 1, 1, 2}, {1, 2, 3, 4}, {2, 0, 2, 0}}; | m1 = NullSpace[A] | m2 = NullSpace[N[A, 16]] | | | Out[190]= {{0, -2, 0, 1}, {-1, -1, 1, 0}} | | Out[191]= | {{0.5286741846941267165032578206`16., -0.4493204281752718232493645376`16., | -0.5286741846941267165032578206`16., | 0.488997306434699269876311179`16.}, | {-0.4183886482487962269364866589`16., -0.78504329244074722971820122`16., | 0.4183886482487962269364866589`16., | 0.1833273220959755013908572806`16.}} | | ------------- | | thanks | Nasser | |