1 files changed, 69 insertions, 0 deletions
diff --git a/tests/iter/tpermutations.nim b/tests/iter/tpermutations.nim
new file mode 100644
index 000000000..30a66460f
--- /dev/null
+++ b/tests/iter/tpermutations.nim
@@ -0,0 +1,69 @@
+discard """
+output: '''
+@[@[1.0, 2.0], @[3.0, 4.0]]
+perm: 10.0 det: -2.0
+@[@[1.0, 2.0, 3.0, 4.0], @[4.0, 5.0, 6.0, 7.0], @[7.0, 8.0, 9.0, 10.0], @[10.0, 11.0, 12.0, 13.0]]
+perm: 29556.0 det: 0.0
+@[@[0.0, 1.0, 2.0, 3.0, 4.0], @[5.0, 6.0, 7.0, 8.0, 9.0], @[10.0, 11.0, 12.0, 13.0, 14.0], @[15.0, 16.0, 17.0, 18.0, 19.0], @[20.0, 21.0, 22.0, 23.0, 24.0]]
+perm: 6778800.0 det: 0.0
+'''
+"""
+
+
+import sequtils, sugar
+
+iterator permutations*[T](ys: openArray[T]): tuple[perm: seq[T], sign: int] =
+  var
+    d = 1
+    c = newSeq[int](ys.len)
+    xs = newSeq[T](ys.len)
+    sign = 1
+
+  for i, y in ys: xs[i] = y
+  yield (xs, sign)
+
+  block outter:
+    while true:
+      while d > 1:
+        dec d
+        c[d] = 0
+      while c[d] >= d:
+        inc d
+        if d >= ys.len: break outter
+
+      let i = if (d and 1) == 1: c[d] else: 0
+      swap xs[i], xs[d]
+      sign *= -1
+      yield (xs, sign)
+      inc c[d]
+
+proc det(a: seq[seq[float]]): float =
+  let n = toSeq 0..a.high
+  for sigma, sign in n.permutations:
+    result += sign.float * n.map((i: int) => a[i][sigma[i]]).foldl(a * b)
+
+proc perm(a: seq[seq[float]]): float =
+  let n = toSeq 0..a.high
+  for sigma, sign in n.permutations:
+    result += n.map((i: int) => a[i][sigma[i]]).foldl(a * b)
+
+for a in [
+    @[ @[1.0, 2.0]
+     , @[3.0, 4.0]
+    ],
+    @[ @[ 1.0,  2,  3,  4]
+     , @[ 4.0,  5,  6,  7]
+     , @[ 7.0,  8,  9, 10]
+     , @[10.0, 11, 12, 13]
+    ],
+    @[ @[ 0.0,  1,  2,  3,  4]
+     , @[ 5.0,  6,  7,  8,  9]
+     , @[10.0, 11, 12, 13, 14]
+     , @[15.0, 16, 17, 18, 19]
+     , @[20.0, 21, 22, 23, 24]
+    ] ]:
+  echo a
+  echo "perm: ", a.perm, " det: ", a.det
+
+# bug #3499 last snippet fixed
+# bug 705  last snippet fixed