From 83576f33cc2c4239d0030441a399e52bc03af6b3 Mon Sep 17 00:00:00 2001
From: Pier-Luc St-Onge <pier-luc.st-onge@calculquebec.ca>
Date: Mon, 13 May 2024 10:09:02 -0400
Subject: [PATCH] =?UTF-8?q?Chap=204=20-=20Collectives=20d'op=C3=A9rations?=
 =?UTF-8?q?=20de=20r=C3=A9duction?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 4-collectives.ipynb | 127 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 124 insertions(+), 3 deletions(-)

diff --git a/4-collectives.ipynb b/4-collectives.ipynb
index 3ea4198..ceb4012 100644
--- a/4-collectives.ipynb
+++ b/4-collectives.ipynb
@@ -232,8 +232,8 @@
     "//     void *recep, int compte_recep, MPI_Datatype type_recep,\n",
     "//     MPI_Comm comm)\n",
     "\n",
-    "ierr = MPI_Alltoall(&a, 1, MPI_INT,\n",
-    "                     b, 1, MPI_INT, MPI_COMM_WORLD);\n",
+    "ierr = MPI_Alltoall(a, 1, MPI_INT,\n",
+    "                    b, 1, MPI_INT, MPI_COMM_WORLD);\n",
     "\n",
     "```"
    ]
@@ -252,10 +252,131 @@
     "```"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "0f692ce2-2b93-4d98-90d7-770c42194d32",
+   "metadata": {},
+   "source": [
+    "## Calculs collectifs\n",
+    "\n",
+    "### Opérations de réduction\n",
+    "\n",
+    "C'est l'équivalent d'un `MPI_Gather` avec une boucle effectuant une\n",
+    "opération de réduction. Voici quelques opérations de réduction :"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "13b3c7bb-b360-484e-83c7-0a0fd976a34f",
+   "metadata": {},
+   "source": [
+    "Opération             | Constante MPI | Op([3, 5])\n",
+    "----------------------|---------------|-----------\n",
+    "Maximum               | `MPI_MAX`     | 5\n",
+    "Minimum               | `MPI_MIN`     | 3\n",
+    "Somme                 | `MPI_SUM`     | 8\n",
+    "Produit               | `MPI_PROD`    | 15\n",
+    "_ET_ logique          | `MPI_LAND`    | Vrai\n",
+    "_OU_ logique          | `MPI_LOR`     | Vrai\n",
+    "_OU exclusif_ logique | `MPI_LXOR`    | Faux\n",
+    "_ET_ binaire          | `MPI_BAND`    | 1 (001 = 011 & 101)\n",
+    "_OU_ binaire          | `MPI_BOR`     | 7 (111 = 011 \\| 101)\n",
+    "_OU exclusif_ binaire | `MPI_BXOR`    | 6 (110 = 011 ^ 101)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "0c69323a-8f71-4002-ab83-b84bb3b3cda4",
+   "metadata": {},
+   "source": [
+    "### Réduction avec `MPI_Reduce`\n",
+    "\n",
+    "Voici un exemple de réduction effectuant une somme :\n",
+    "\n",
+    "![Figure MPI_Reduce](images/mpi_reduce.svg)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "0d37767c-ae8c-4c48-8136-630b23a758d1",
+   "metadata": {},
+   "source": [
+    "[En **C**](https://www.mpi-forum.org/docs/mpi-4.1/mpi41-report.pdf#subsection.6.9.1) :\n",
+    "\n",
+    "```C\n",
+    "// int MPI_Reduce(\n",
+    "//     void *envoi, void *recep, int compte, MPI_Datatype type,\n",
+    "//     MPI_Op op, int racine, MPI_Comm comm)\n",
+    "\n",
+    "ierr = MPI_Reduce(&a, &b, 1, MPI_INT,\n",
+    "                  MPI_SUM, 2, MPI_COMM_WORLD);\n",
+    "\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f61ea7f9-bab2-41ad-bd86-935121248dbe",
+   "metadata": {},
+   "source": [
+    "[En **Python**](https://mpi4py.readthedocs.io/en/latest/reference/mpi4py.MPI.Comm.html#mpi4py.MPI.Comm.reduce) :\n",
+    "\n",
+    "```Python\n",
+    "# reduce(envoi: Any, op: Op=SUM, racine: int = 0) -> Any | None\n",
+    "\n",
+    "b = comm.reduce(a, MPI.SUM, 2)\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "af055858-a980-4077-81c5-11e2997ed3d4",
+   "metadata": {},
+   "source": [
+    "### Réduction et diffusion avec `MPI_Allreduce`\n",
+    "\n",
+    "C'est l'équivalent de `MPI_Reduce` + `MPI_Bcast`,\n",
+    "mais en plus efficace :\n",
+    "\n",
+    "![Figure MPI_Allreduce](images/mpi_allreduce.svg)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5ce781ab-c1a5-4a62-b9f8-cd5c039e0f0a",
+   "metadata": {},
+   "source": [
+    "[En **C**](https://www.mpi-forum.org/docs/mpi-4.1/mpi41-report.pdf#subsection.6.9.6) :\n",
+    "\n",
+    "```C\n",
+    "// int MPI_Allreduce(\n",
+    "//     void *envoi, void *recep, int compte, MPI_Datatype type,\n",
+    "//     MPI_Op op, MPI_Comm comm)\n",
+    "\n",
+    "ierr = MPI_Allreduce(&a, &b, 1, MPI_INT,\n",
+    "                     MPI_SUM, MPI_COMM_WORLD);\n",
+    "\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f23cf72c-4e33-458e-95b2-0e492a8b7dca",
+   "metadata": {},
+   "source": [
+    "[En **Python**](https://mpi4py.readthedocs.io/en/latest/reference/mpi4py.MPI.Comm.html#mpi4py.MPI.Comm.allreduce) :\n",
+    "\n",
+    "```Python\n",
+    "# allreduce(envoi: Any, op: Op=SUM) -> Any\n",
+    "\n",
+    "b = comm.allreduce(a, MPI.SUM)\n",
+    "```"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a7085b5e-bf34-48b3-ba80-f2e3d9de1fc2",
+   "id": "2477c068-510f-48a6-b56e-24c0d911a60e",
    "metadata": {},
    "outputs": [],
    "source": []