/* return a bound for T_2(P), P | polbase in C[X]
* NB: Mignotte bound: A | S ==>
* |a_i| <= binom(d-1, i-1) || S ||_2 + binom(d-1, i) lc(S)
*
* Apply to sigma(S) for all embeddings sigma, then take the L_2 norm over
* sigma, then take the sup over i.
**/
static GEN
nf_Mignotte_bound(GEN nf, GEN polbase)
{
GEN G = gmael(nf,5,2), lS = leading_term(polbase); /* t_INT */
GEN p1, C, N2, matGS, binlS, bin;
long prec, i, j, d = degpol(polbase), n = degpol(nf[1]), r1 = nf_get_r1(nf);
binlS = bin = vecbinome(d-1);
if (!gcmp1(lS)) binlS = gmul(lS, bin);
N2 = cgetg(n+1, t_VEC);
prec = gprecision(G);
for (;;)
{
nffp_t F;
matGS = cgetg(d+2, t_MAT);
for (j=0; j<=d; j++) gel(matGS,j+1) = arch_for_T2(G, gel(polbase,j+2));
matGS = shallowtrans(matGS);
for (j=1; j <= r1; j++) /* N2[j] = || sigma_j(S) ||_2 */
{
gel(N2,j) = gsqrt( QuickNormL2(gel(matGS,j), DEFAULTPREC), DEFAULTPREC );
if (lg(N2[j]) < DEFAULTPREC) goto PRECPB;
}
for ( ; j <= n; j+=2)
{
GEN q1 = QuickNormL2(gel(matGS,j ), DEFAULTPREC);
GEN q2 = QuickNormL2(gel(matGS,j+1), DEFAULTPREC);
p1 = gmul2n(mpadd(q1, q2), -1);
gel(N2,j) = gel(N2,j+1) = gsqrt( p1, DEFAULTPREC );
if (lg(N2[j]) < DEFAULTPREC) goto PRECPB;
}
if (j > n) break; /* done */
PRECPB:
prec = (prec<<1)-2;
remake_GM(nf, &F, prec); G = F.G;
if (DEBUGLEVEL>1) pari_warn(warnprec, "nf_factor_bound", prec);
}
/* Take sup over 0 <= i <= d of
* sum_sigma | binom(d-1, i-1) ||sigma(S)||_2 + binom(d-1,i) lc(S) |^2 */
/* i = 0: n lc(S)^2 */
C = mulsi(n, sqri(lS));
/* i = d: sum_sigma ||sigma(S)||_2^2 */
p1 = gnorml2(N2); if (gcmp(C, p1) < 0) C = p1;
for (i = 1; i < d; i++)
{
GEN s = gen_0;
for (j = 1; j <= n; j++)
{
p1 = mpadd( mpmul(gel(bin,i), gel(N2,j)), gel(binlS,i+1) );
s = mpadd(s, gsqr(p1));
}
if (gcmp(C, s) < 0) C = s;
}
return C;
}
static GEN
bnflog_i(GEN bnf, GEN ell)
{
long prec0, prec;
GEN nf, US, vdegS, S, T, M, CLp, CLt, Ftilde, vtG, ellk;
GEN D, Ap, cycAp, bnfS;
long i, j, lS, lvAp;
checkbnf(bnf);
nf = checknf(bnf);
S = idealprimedec(nf, ell);
bnfS = bnfsunit0(bnf, S, nf_GENMAT, LOWDEFAULTPREC); /* S-units */
US = leafcopy(gel(bnfS,1));
prec0 = maxss(30, vtilde_prec(nf, US, ell));
US = shallowconcat(bnf_get_fu(bnf), US);
settyp(US, t_COL);
T = padicfact(nf, S, prec0);
lS = lg(S); Ftilde = cgetg(lS, t_VECSMALL);
for (j = 1; j < lS; j++) Ftilde[j] = ftilde(nf, gel(S,j), gel(T,j));
CLp = CL_prime(bnf, ell, S);
cycAp = gel(CLp,1);
Ap = gel(CLp,2);
for(;;)
{
CLt = CL_tilde(nf, US, ell, T, Ftilde, &vtG, prec0);
if (CLt) break;
prec0 <<= 1;
T = padicfact(nf, S, prec0);
}
prec = ellexpo(cycAp, ell) + ellexpo(CLt,ell) + 1;
if (prec == 1) return mkvec3(cgetg(1,t_VEC), cgetg(1,t_VEC), cgetg(1,t_VEC));
vdegS = get_vdegS(Ftilde, ell, prec0);
ellk = powiu(ell, prec);
lvAp = lg(Ap);
if (lvAp > 1)
{
GEN Kcyc = bnf_get_cyc(bnf);
GEN C = zeromatcopy(lvAp-1, lS-1);
GEN Rell = gel(CLp,3), Uell = gel(CLp,4), ordS = gel(CLp,5);
for (i = 1; i < lvAp; i++)
{
GEN a, b, bi, A = gel(Ap,i), d = gel(cycAp,i);
bi = isprincipal(bnf, A);
a = vecmodii(ZC_Z_mul(bi,d), Kcyc);
/* a in subgroup generated by S = Rell; hence b integral */
b = hnf_invimage(Rell, a);
b = vecmodii(ZM_ZC_mul(Uell, ZC_neg(b)), ordS);
A = mkvec2(A, cgetg(1,t_MAT));
A = idealpowred(nf, A, d);
/* find a principal representative of A_i^cycA_i up to elements of S */
a = isprincipalfact(bnf,gel(A,1),S,b,nf_GENMAT|nf_FORCE);
if (!gequal0(gel(a,1))) pari_err_BUG("bnflog");
a = famat_mul_shallow(gel(A,2), gel(a,2)); /* principal part */
if (lg(a) == 1) continue;
for (j = 1; j < lS; j++)
gcoeff(C,i,j) = vtilde(nf, a, gel(T,j), gel(vdegS,j), ell, prec0);
}
C = gmod(gneg(C),ellk);
C = shallowtrans(C);
M = mkmat2(mkcol2(diagonal_shallow(cycAp), C), mkcol2(gen_0, vtG));
M = shallowmatconcat(M); /* relation matrix */
}
else
M = vtG;
M = ZM_hnfmodid(M, ellk);
D = matsnf0(M, 4);
if (lg(D) == 1 || !dvdii(gel(D,1), ellk))
pari_err_BUG("bnflog [missing Z_l component]");
D = vecslice(D,2,lg(D)-1);
return mkvec3(D, CLt, ellsylow(cycAp, ell));
}
