Re: Position and Real Numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg18907] Re: Position and Real Numbers*From*: Paul Abbott <paul at physics.uwa.edu.au>*Date*: Mon, 26 Jul 1999 14:27:47 -0400*Organization*: University of Western Australia*References*: <7n694d$h5o@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Jason Gill wrote: > Is there an easy way to make Position work as expected for real numbers, or more > accurately make Range work as > expected ??? Both work "as expected". With In[1]:= x=Range[-3,2,.05]; since the elements are distinct, to locate -0.05 you could use a test such as In[2]:= Position[x,_?(-0.06<#<-0.04&)] Out[2]= {{60}} or you could Rationalize the entries In[3]:= Position[Rationalize[x],Rationalize[-1/20]] Out[3]= {{60}} You can make Range give a set of exact values if you give it exact input: In[4]:= x=Range[-3,2,Rationalize[0.05]]; In[5]:= Position[x,Rationalize[-1/20]] Out[5]= {{60}} Moral: If you give Mathematica exact input and it will generally give you exact ouput. With approximate input you generally get approximate output. ____________________________________________________________________ Paul Abbott Phone: +61-8-9380-2734 Department of Physics Fax: +61-8-9380-1014 The University of Western Australia Nedlands WA 6907 mailto:paul at physics.uwa.edu.au AUSTRALIA http://physics.uwa.edu.au/~paul God IS a weakly left-handed dice player ____________________________________________________________________