From 45ecbc5f2ee2cf4935d8d8f771b349d3b3ae0a2d Mon Sep 17 00:00:00 2001
From: ap02323 <ap02323.surrey.ac.uk>
Date: Fri, 20 Oct 2023 16:55:57 +0100
Subject: [PATCH] pbcost default values set to inf

In the custom loop example, the objective function is called twice, which is a problem for computationally expensive objective functions, only because the array of personal best did not have default values for the first iteration. This has been fixed by setting the default values of pbcost to inf.
---
 .../tutorials/custom_optimization_loop.ipynb        | 13 ++++++-------
 pyswarms/backend/swarms.py                          |  5 ++++-
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/docs/examples/tutorials/custom_optimization_loop.ipynb b/docs/examples/tutorials/custom_optimization_loop.ipynb
index 51b1ae6e..413c4d53 100644
--- a/docs/examples/tutorials/custom_optimization_loop.ipynb
+++ b/docs/examples/tutorials/custom_optimization_loop.ipynb
@@ -111,13 +111,13 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Iteration: 1 | my_swarm.best_cost: 0.0009\n",
+      "Iteration: 1 | my_swarm.best_cost: 0.0070\n",
       "Iteration: 21 | my_swarm.best_cost: 0.0000\n",
       "Iteration: 41 | my_swarm.best_cost: 0.0000\n",
       "Iteration: 61 | my_swarm.best_cost: 0.0000\n",
       "Iteration: 81 | my_swarm.best_cost: 0.0000\n",
       "The best cost found by our swarm is: 0.0000\n",
-      "The best position found by our swarm is: [3.30572365e-19 2.93696483e-19]\n"
+      "The best position found by our swarm is: [1.77943664e-18 2.49653561e-18]\n"
      ]
     }
    ],
@@ -126,7 +126,6 @@
     "for i in range(iterations):\n",
     "    # Part 1: Update personal best\n",
     "    my_swarm.current_cost = f(my_swarm.position) # Compute current cost\n",
-    "    my_swarm.pbest_cost = f(my_swarm.pbest_pos)  # Compute personal best pos\n",
     "    my_swarm.pbest_pos, my_swarm.pbest_cost = P.compute_pbest(my_swarm) # Update and store\n",
     "    \n",
     "    # Part 2: Update global best\n",
@@ -163,15 +162,15 @@
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "2019-05-18 15:39:20,737 - pyswarms.single.global_best - INFO - Optimize for 100 iters with {'c1': 0.6, 'c2': 0.3, 'w': 0.4}\n",
-      "pyswarms.single.global_best: 100%|██████████|100/100, best_cost=0.00418\n",
-      "2019-05-18 15:39:21,942 - pyswarms.single.global_best - INFO - Optimization finished | best cost: 0.004177699645933291, best pos: [0.03663518 0.05325001]\n"
+      "2023-10-20 14:44:14,240 - pyswarms.single.global_best - INFO - Optimize for 100 iters with {'c1': 0.6, 'c2': 0.3, 'w': 0.4}\n",
+      "pyswarms.single.global_best: 100%|██████████|100/100, best_cost=0.00596\n",
+      "2023-10-20 14:44:14,358 - pyswarms.single.global_best - INFO - Optimization finished | best cost: 0.0059581279236955356, best pos: [0.04219012 0.06463839]\n"
      ]
     },
     {
      "data": {
       "text/plain": [
-       "(0.004177699645933291, array([0.03663518, 0.05325001]))"
+       "(0.0059581279236955356, array([0.04219012, 0.06463839]))"
       ]
      },
      "execution_count": 4,
diff --git a/pyswarms/backend/swarms.py b/pyswarms/backend/swarms.py
index f3817cb3..e41a34d2 100644
--- a/pyswarms/backend/swarms.py
+++ b/pyswarms/backend/swarms.py
@@ -96,7 +96,6 @@ class Swarm(object):
     )
     pbest_cost = attrib(
         type=np.ndarray,
-        default=np.array([]),
         validator=instance_of(np.ndarray),
     )
     best_cost = attrib(
@@ -119,3 +118,7 @@ def dimensions_default(self):
     @pbest_pos.default
     def pbest_pos_default(self):
         return self.position
+    
+    @pbest_cost.default
+    def pbest_cost_default(self):
+        return np.full(shape=(self.position.shape[0],), fill_value=np.inf)