From 4d4ab9936b63e86144b3a421e6937feec2fa2d56 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Ne=C4=8Dada?= <marek@necada.org>
Date: Sun, 25 Aug 2019 21:17:23 +0300
Subject: [PATCH] =?UTF-8?q?Variable=20Lov=C3=A1sz=20condition=20parameter?=
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Former-commit-id: 726d5c1b1dc03a5b11f8d7b32e6bf589efec369d
---
 qpms/lattices.h     | 3 ++-
 qpms/lll.c          | 5 +++--
 qpms/qpms_c.pyx     | 4 ++--
 qpms/qpms_cdefs.pxd | 2 +-
 4 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/qpms/lattices.h b/qpms/lattices.h
index b9c28dd..45a7322 100644
--- a/qpms/lattices.h
+++ b/qpms/lattices.h
@@ -72,7 +72,8 @@ static inline point2d point2d_fromxy(const double x, const double y) {
  */
 int qpms_reduce_lattice_basis(double *b, ///< Array of dimension [bsize][ndim].
 		const size_t bsize, ///< Number of the basis vectors (dimensionality of the lattice).
-		const size_t ndim ///< Dimension of the space into which the lattice is embedded.
+		const size_t ndim, ///< Dimension of the space into which the lattice is embedded.
+		double delta
 		);
 
 /// Generic lattice point generator type.
diff --git a/qpms/lll.c b/qpms/lll.c
index 02fc0da..bf381fa 100644
--- a/qpms/lll.c
+++ b/qpms/lll.c
@@ -38,7 +38,8 @@ static void gram_schmidt(
 static inline double fsq(double x) { return x * x; };
 
 // A naïve implementation of Lenstra-Lenstra-Lovász algorithm.
-int qpms_reduce_lattice_basis(double *b, const size_t bsize, const size_t ndim)
+int qpms_reduce_lattice_basis(double *b, const size_t bsize, const size_t ndim, 
+    double delta)
 {
   QPMS_ENSURE(bsize <= ndim, 
       "The basis must have less elements (%zd) than the space dimension (%zd).",
@@ -59,7 +60,7 @@ int qpms_reduce_lattice_basis(double *b, const size_t bsize, const size_t ndim)
     }
     // Step 2
     if (k > 0 && // Case 1
-        bstar_sqnorm[k] < (0.75 - fsq(mu[mu_index(k, k-1)])) * bstar_sqnorm[k-1]) {
+        bstar_sqnorm[k] < (delta - fsq(mu[mu_index(k, k-1)])) * bstar_sqnorm[k-1]) {
       // swap b(k) and b(k-1)
       cblas_dswap(ndim, &b[k*ndim], 1, &b[(k-1)*ndim], 1);
       double B_k = bstar_sqnorm[k];
diff --git a/qpms/qpms_c.pyx b/qpms/qpms_c.pyx
index cfb6218..6e7ba36 100644
--- a/qpms/qpms_c.pyx
+++ b/qpms/qpms_c.pyx
@@ -610,7 +610,7 @@ def gamma_inc_CF(double a, cdouble x):
         cx_gamma_inc_CF_e(a, x, &res)
     return (res.val, res.err)
 
-def lll_reduce(basis):
+def lll_reduce(basis, double delta=0.75):
     """
     Lattice basis reduction with the Lenstra-Lenstra-Lovász algorithm.
 
@@ -630,7 +630,7 @@ def lll_reduce(basis):
                 "the dimensionality of the lattice (%d) embedded into it."
                 % (d, n))
     cdef double [:,:] basis_view = basis
-    if 0 != qpms_reduce_lattice_basis(&basis_view[0,0], n, d):
+    if 0 != qpms_reduce_lattice_basis(&basis_view[0,0], n, d, delta):
         raise RuntimeError("Something weird happened")
     return basis
 
diff --git a/qpms/qpms_cdefs.pxd b/qpms/qpms_cdefs.pxd
index 9987119..940c7f0 100644
--- a/qpms/qpms_cdefs.pxd
+++ b/qpms/qpms_cdefs.pxd
@@ -209,7 +209,7 @@ cdef extern from "lattices.h":
         PGEN_1D_INC_TOWARDS_ORIGIN
     PGen PGen_1D_new_minMaxR(double period, double offset, double minR, bint inc_minR,
             double maxR, bint inc_maxR, PGen_1D_incrementDirection incdir)
-    int qpms_reduce_lattice_basis(double *b, size_t bsize, size_t ndim)
+    int qpms_reduce_lattice_basis(double *b, size_t bsize, size_t ndim, double delta)
 
 
 cdef extern from "quaternions.h":