check coprimality of moduli in CRT_basis()

sagemath · Oct 12, 2023 · 06955d9 · 06955d9
1 parent 2f1a76d
commit 06955d9
Showing 1 changed file with 8 additions and 5 deletions.
diff --git a/src/sage/arith/misc.py b/src/sage/arith/misc.py
@@ -3579,10 +3579,6 @@ def CRT_basis(moduli):
  `a_i` is congruent to 1 modulo `m_i` and to 0 modulo `m_j` for
  `j\not=i`.
 
- .. note::
-
- The pairwise coprimality of the input is not checked.
-
  EXAMPLES::
 
  sage: a1 = ZZ(mod(42,5))
@@ -3605,7 +3601,14 @@ def CRT_basis(moduli):
  if n == 0:
  return []
  M = prod(moduli)
- return [((xgcd(m,M//m)[2])*(M//m)) % M for m in moduli]
+ cs = []
+ for m in moduli:
+ Mm = M//m
+ d,_,v = xgcd(m,Mm)
+ if not d.is_one():
+ raise ValueError('moduli must be coprime')
+ cs.append(v * Mm % M)
+ return cs
 
 
 def CRT_vectors(X, moduli):