R: Re: Re: Modify machine precision

[alberto frigerio]

No problem :)

Attached you will find the Input data, my results and my friend one. As you might see, they are very similar but not the same.

With matrix X and vector w, the result is given by r = X' * (prod(X*w')./(X*w')); .

Jordi, you are right, I try to explain better what I mean. 
eps is the smallest number so that alpha + eps <> alpha. Is there a way to say Octave "Look, I don't want eps to be your default value no more, please use for the function I'm running now this neweps value" ? Obviously it doesn't work if I simpy assign eps = neweps in the script file. I don't know if using my friend precision I will reach his solution, but I do not have any other way to check it ...

Thanks everyone,

   Alberto

Il 29/03/12, Nicholas Jankowski  <address@hidden> ha scritto:

Alberto: just so we're clear, could you provide a concise example of
the data you're working with and what you're trying to do with it?
Before we send you off to a Maxima or Mathematica solution, it would
be good to verify that the problem here isn't just definitions or
communication. :)

nickj

2012/3/29 Jordi Gutiérrez Hermoso <address@hidden>:
> 2012/3/29 alberto frigerio <address@hidden>:
>> So you are telling me that in Octave there is no way to force machine
>> precision in a program? My problem is that I'm doing some analyses with
>> another precision whose machine precision is 1e-13
>
> Listen to what you just said. Programs have different *machine*
> precision? The *machine* precision isn't determined by software, but
> it's a property of your hardware, of your *machine*. Your computer has
> an FPU, and this FPU has certain limitations:
>
>    http://en.wikipedia.org/wiki/Floating-point_unit
>
> If you need variable precision arithmetic, you can try to use vpa from
> the symbolic package, but depending on what you're doing, I would
> follow Martin Helm's recommendation and use a program other than
> Octave.
>
> HTH,
> - Jordi G. H.
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://mailman.cae.wisc.edu/listinfo/help-octave

InputMat.txt
Description: Text document

InputVec.txt
Description: Text document

ResultFriend.txt
Description: Text document

ResultOctave.txt
Description: Text document