reverse of digits()

[Mathieu Carbou <mathieu.carbou@gmail.com>]

Hello,

I've seen the new digits() and sumdigits() functions. I was wondering if there was also the reverse function of digits (i.e. vectonum([1,2,3,4,5], 10) == 12345) plus these functions which could be useful ;-)

Thank you !

/*
    Digit decomposition of n in base b by ascending order of b exponents. I.e. digits(12345) == [1,2,3,4,5]
*/
vectonum(v, b=10) =
{
    my(n=0);
    for(i=1,#v, n+=v[i]*b^(#v-i));
    return(n);
}

/*
    Number of digits of n in base b
*/
ndigits(n, b=10) =
{
    my(c=0);
    if(n==0, return(1));
    while(n, n=n\b; c++);
    return(c);
}

/*
    Representation of n in factoradic base b.
    The number n is taken modulo b!
*/
factoradic(n, b=10) =
{
    my(v=vector(b), qr=[0,n%(b!)]);
    for(i=1, b, qr=divrem(qr[2], (b-i)!); v[i]=qr[1]);
    return(v);
}

--

Mathieu Carbou
Cell: 514-660-4287