- include <stdio.h>
/* adapted from 'Notation as a Tool of Thought', by K.E.Iverson
Radix Representation of Permutations
- /
/* direct from radix; of given order */ dfr(short direct[?,short radix[?,long order) {
if (order) {
direct[0? = radix[0?; dfr (direct+1, radix+1, order-1); while (--order)
}
}
/* radix representation; of given order and given index */ rr(short radix[?, long order, long index) {
int i;
for (i=1; i<=order; i++) {
radix[order-i? = index % i; index = index/i;
}
}
show(short perm[?,long order) {
while(order--)
printf("%hd ",*perm++);
printf("\n");
}
short parity(short radix[?,long order) {
long p=0;
while(order--)
p+=*radix++;
return p%2;
}
void usage(char *name) {
fprintf(stderr,"usage: %s order number_of_permutation\n",name); exit(-1);
}
main(int argc, char *argv[?) {
define MAX_ORDER 512
short radix[MAX_ORDER?, direct[MAX_ORDER?; long order, nth;
if (argc!=3) usage(argv[0?); order = atol(argv[1?); nth = atol(argv[2?); rr(radix, order, nth-1); /* where 0 is the first permuatation */ dfr(direct, radix, order);
printf("radix "); show(radix,order); printf("direct "); show(direct,order); printf("parity %d\n",parity(radix,order));
}
--
J. Henri Schueler, H&h Software, Toronto +1 416 698 9075 jhs@ipsa.reuter.com