From f723ec876aa45ae68a7317385f340648ff0beed6 Mon Sep 17 00:00:00 2001
From: KlausC <klausC@users.noreply.github.com>
Date: Tue, 10 Sep 2024 16:03:07 +0200
Subject: [PATCH] hermite normal form fixed

---
 src/determinant.jl | 130 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 121 insertions(+), 9 deletions(-)

diff --git a/src/determinant.jl b/src/determinant.jl
index 5c80830..b163eba 100644
--- a/src/determinant.jl
+++ b/src/determinant.jl
@@ -330,7 +330,7 @@ function det_MV(a::AbstractMatrix{D}) where D<:Union{Ring,Integer}
 end
 
 
-#TODO fix algorithm. normal forms to dedicated file
+#TODO normal forms to dedicated file
 """
     hermite_normal_form(A::AbstractMatrix; column_style=true, round=RoundUp) -> H, U
 
@@ -349,7 +349,11 @@ See [Wiki](https://en.wikipedia.org/wiki/Hermite_normal_form)
 
 The algorithm was generalized to matrices of arbitrary rank and shape.
 """
-function hermite_normal_form(a::AbstractMatrix{R}; column_style::Bool=true, round::RoundingMode=RoundUp) where R<:Union{Ring,Integer}
+function hermite_normal_form(
+    a::AbstractMatrix{R};
+    column_style::Bool = true,
+    round::RoundingMode = RoundUp,
+) where R<:Union{Ring,Integer}
     m, n = size(a)
 
     if column_style
@@ -362,7 +366,11 @@ function hermite_normal_form(a::AbstractMatrix{R}; column_style::Bool=true, roun
     end
 end
 
-function hermite_normal_form!(a::AbstractMatrix{R}, u::AbstractMatrix{R}, round::RoundingMode) where R
+function hermite_normal_form!(
+    a::AbstractMatrix{R},
+    u::AbstractMatrix{R},
+    round::RoundingMode,
+) where R
     m, n = size(a)
     piv = something.(findfirst.(!iszero, eachcol(a)), m + 1)
     n = something(findlast(x -> x <= m, piv), 0)
@@ -386,11 +394,7 @@ function hermite_normal_form!(a::AbstractMatrix{R}, u::AbstractMatrix{R}, round:
                 elseif pi == pj && pi <= m
                     ajj = a[pj, j]
                     aji = a[pj, i]
-                    r, p, q = gcdx(ajj, aji)
-                    @assert !iszero(r)
-                    #@assert max(abs(p), abs(q)) <= max(abs(ajj), abs(aji))
-                    pp = -div(aji, r)
-                    qq = div(ajj, r)
+                    r, q, p, qq, pp = gcdex(aji, ajj)
                     for k = 1:m
                         akj = a[k, j]
                         aki = a[k, i]
@@ -399,7 +403,7 @@ function hermite_normal_form!(a::AbstractMatrix{R}, u::AbstractMatrix{R}, round:
                         a[k, j] = bkj
                         a[k, i] = bki
                     end
-                    for k = 1:n
+                    for k = 1:size(u, 1)
                         akj = u[k, j]
                         aki = u[k, i]
                         bkj = akj * p + aki * q
@@ -418,6 +422,13 @@ function hermite_normal_form!(a::AbstractMatrix{R}, u::AbstractMatrix{R}, round:
     a, u
 end
 
+function gcdex(a, b)
+    r, p, q = gcdx(a, b)
+    pp = -div(b, r)
+    qq = div(a, r)
+    r, p, q, pp, qq
+end
+
 function swap(a::AbstractMatrix, i, j)
     m = size(a, 1)
     for k = 1:m
@@ -448,3 +459,104 @@ end
 
 Base.div(a::T, b::T, round::RoundingMode) where T<:ZZ = T(div(value(a), value(b), round))
 Base.div(a::T, b::T, ::RoundingMode) where T<:Ring = div(a, b)
+
+#
+# u, v unimodular, d diagonal with mod(d[i+1,i+1], d[i,i]) == 0
+# u * a * v = d
+function smith_normal!(a::AbstractMatrix, u::AbstractMatrix, v::AbstractMatrix)
+    b = copy(a)
+    m, n = size(a)
+    m == size(u, 1) || throw(DimensionMismatch("left square matrix"))
+    n == size(v, 2) || throw(DimensionMismatch("right square matrix"))
+    i = 1
+    while i <= min(m, n)
+        A = view(a, i:m, i:n)
+        U = view(u, i:m, 1:size(u, 2))
+        V = view(v, 1:size(v, 1), i:n)
+
+        hermite_normal_form!(A, V, RoundUp)
+        swap_zero_rows!(A, U)
+        stop = false
+        while !stop
+            hermite_left!(A, U)
+            hermite_normal_form!(A, V, RoundUp)
+            stop = is_unit_column(A)
+            if stop
+                k = first_non_multiple_column(A)
+                stop = k == 0
+                if k > 1
+                    A[:, 1] .+= A[:, k]
+                    V[:, 1] .+= V[:, k]
+                end
+            end
+        end
+        i += 1
+    end
+    u, a, v
+end
+
+function hermite_left!(a, u)
+    m, n = size(a)
+    j = 1
+    for i = 2:m
+        aij = a[i, j]
+        iszero(aij) && continue
+        ajj = a[j, j]
+        g, q, p, qq, pp = gcdex(aij, ajj)
+        for k = 1:n
+            akj = a[j, k]
+            aki = a[i, k]
+            bkj = akj * p + aki * q
+            bki = akj * pp + aki * qq
+            a[j, k] = bkj
+            a[i, k] = bki
+        end
+        for k = 1:size(u, 2)
+            akj = u[j, k]
+            aki = u[i, k]
+            bkj = akj * p + aki * q
+            bki = akj * pp + aki * qq
+            u[j, k] = bkj
+            u[i, k] = bki
+        end
+    end
+end
+
+function swap_zero_rows!(A, U)
+    m, n = size(A)
+    k = 1
+    while k <= m && iszero(A[k, 1])
+        k += 1
+    end
+    if k > 1
+        for j = k:m
+            A[j-k+1, :] .= A[j, :]
+            A[j, :] .= 0
+            for i = 1:size(U, 2)
+                ukk = U[j-k+1, i]
+                U[j-k+1, i] = U[j, i]
+                U[j, i] = ukk
+            end
+        end
+    end
+end
+
+function is_unit_column(A)
+    iszero(A[2:size(A, 1), 1])
+end
+
+function isunit(a::Integer)
+    abs(a) == 1
+end
+
+function first_non_multiple_column(A)
+    m, n = size(A)
+    akk = A[1, 1]
+    for j = 1:n
+        for i = j:m
+            aij = A[i, j]
+            iszero(aij) || iszero(mod(aij, akk)) || return j
+        end
+    end
+    return 0
+end