Fwd: qfunc/qfuncinv implementation in communications package

[Richardson, Anthony]

 

 

------ Original Message ------
From: Przemek Klosowski
Date: 1/24/2013 3:05 PM
To: address@hidden;
Subject: Re: qfunc/qfuncinv implementation in communications package

 

On 01/24/2013 02:26 PM, Richardson, Anthony wrote:
> The function qfunc() in the communications package is currently
> implemented as:
>
> y = 1-normcdf(x);
>
> This returns 0 for values of x greater than approx. 8 (where normcdf()
> is close to 1).  I believe a better implementation is:
>
> y = erfc(x/sqrt(2))/2;
>
> A simple test to compare the two implementations is:
>
> x = [0:3:18]; [qfunc(x); erfc(x/sqrt(2))/2]
>


Octave 3.6.3 returns zero for both forms:
[x=[0:3:18]' qfunc(x) erfc(x/sqrt(2))/2]

     0.000000000000000    0.500000000000000    0.500000000000000
     3.000000000000000    0.001349898031630    0.001349898031630
     6.000000000000000    0.000000000986588    0.000000000986588
     9.000000000000000    0.000000000000000    0.000000000000000
    12.000000000000000    0.000000000000000    0.000000000000000
    15.000000000000000    0.000000000000000    0.000000000000000
    18.000000000000000    0.000000000000000    0.000000000000000

_______________________________________________
Are you using the default display "format"  (scientific notation)?

 

Tony