Zero times a variable in numerical calculations

*To*: mathgroup at smc.vnet.net*Subject*: [mg68395] Zero times a variable in numerical calculations*From*: "Maurits Haverkort" <Haverkort at ph2.uni-koeln.de>*Date*: Thu, 3 Aug 2006 06:07:28 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Dear All I have the following problem. In: 0.0 a Out 0. a I would like to have that In: 0.0 a Simplifies to Out: 0 SetPrecision[0.0 a,10^-100] works, but I am a bit puzzled 0.0 ====0 returns true 0.0 a ==== 0 a returns unevaluated to 0.0 a ==== 0 This seems inconsistent to me. 1) Could anyone explain me the logic behind this? 2) What is the fastest way to multiply a numerical matrix times a half numerical half analytical sparse matrix, whereby the result is band diagonal. (The current result has 0. a + 0. b + 0. c + 0. d + 0. e + 0. f on all places where it should be zero.) Thanks in advance. Maurits Haverkort