Re: qfunc/qfuncinv implementation in communications package

[Przemek Klosowski]

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