From 5e3f12beb511fe0a4ecca129efc350c4bbe0b507 Mon Sep 17 00:00:00 2001
From: Sam Hadow <sam.hadow@inbox.lv>
Date: Wed, 2 Apr 2025 15:12:55 +0200
Subject: [PATCH] create lattice

---
 src/matrix.rs | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/matrix.rs b/src/matrix.rs
index b0f36e1..6558e6e 100644
--- a/src/matrix.rs
+++ b/src/matrix.rs
@@ -16,8 +16,26 @@ impl Matrix {
             None
         }
     }
-}
 
+    pub fn new_lattice(noise_bits: usize, ciphertexts: Vec<Element>) -> Option<Self> {
+        let n = ciphertexts.len();
+        let mut values = Vec::with_capacity(n * n);
+
+        // First row: [2^noise_bits, ciphertexts[0], ciphertexts[1], ..., ciphertexts[t]]
+        values.push((2.0f64).powi(noise_bits as i32));
+        values.extend_from_slice(&ciphertexts[1..]);
+
+        // -x0 on diagonal, 0 everywhere else
+        let x0 = ciphertexts[0];
+        for i in 0..n - 1 {
+            let mut row = vec![0.0; n];
+            row[i] = -x0;
+            values.extend(row);
+        }
+
+        Matrix::new(n, values)
+    }
+}
 
 impl Index<(usize, usize)> for Matrix {
     type Output = f64;
@@ -32,7 +50,6 @@ impl IndexMut<(usize, usize)> for Matrix {
     }
 }
 
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -56,4 +73,19 @@ mod tests {
         m[(1, 0)] = 5.0;
         assert_eq!(m[(1, 0)], 5.0);
     }
+    #[test]
+    fn test_new_lattice() {
+        let ciphertexts = vec![5.0, 8.0, 12.0]; // x0=5.0, x1=8.0, x2=12.0
+        let noise_bits = 2;
+
+        // Expected matrix (3x3):
+        // [ 2^2,   x1,   x2 ] = [4.0, 8.0, 12.0]
+        // [ -x0,    0,    0 ] = [-5.0, 0.0, 0.0]
+        // [   0,  -x0,    0 ] = [0.0, -5.0, 0.0]
+        let expected_values = vec![4.0, 8.0, 12.0, -5.0, 0.0, 0.0, 0.0, -5.0, 0.0];
+
+        let lattice = Matrix::new_lattice(noise_bits, ciphertexts).unwrap();
+        assert_eq!(lattice.n, 3);
+        assert_eq!(lattice.values, expected_values);
+    }
 }