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Re: Increasing precision in octave
From: |
Miroslaw Kwasniak |
Subject: |
Re: Increasing precision in octave |
Date: |
Wed, 25 Jun 2008 11:35:09 +0200 |
User-agent: |
Mutt/1.5.9i |
On Fri, Jun 20, 2008 at 06:09:23PM +0400, DimitryASuplatov wrote:
> Hello,
> I want to calculate the p-value with high precision.
> I mean that when I use normal_cdf function I get
>
> normal_cdf (real(24),m,s)
> ans = 1
Are you sure you need such result?
p=
0.99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999986096078814503
;)
>
> and "1" is not enough precision for me. I want to see something like
> 0.999999999999999999999888
p=1-erfc(24/sqrt(2))/2
in octave3 you can use
p=1-erf_Q(24)
but because erf_Q(24)=1.3904e-127 is so small than 1-1.3904e-127 = 1
> How to do that?
If you really need such precision switch to another tool that allow an arbitrary
precision. An example is pari-gp:
? default(realprecision,1000);default(format,"g0.28")
? x=24;y=(erfc(x/sqrt(2))/2)
%49 = 1.390392118549703059565827412 E-127
? x=100;y=(erfc(x/sqrt(2))/2)
%50 = 1.344179076744198305073080167 E-2174