upload chapter 21 new file

try to fix the issue github can't recognize the json format from nb format

Author: xieliaing

chapters/21 第二十一章 元学习器.ipynb

@@ -337,21 +337,8 @@
     "m0 = LGBMRegressor(max_depth=2, min_child_samples=60)\n",
     "m1 = LGBMRegressor(max_depth=2, min_child_samples=60)\n",
     "\n",
-<<<<<<< e022085c519423acf68e0d4c26b60d477788305d
-    "# fit the propensity score model\n",
-    "ps_m = LogisticRegression(solver=\"lbfgs\", penalty='none')\n",
-    "ps_m.fit(train[X], train[T])\n",
-    "ps_score = ps_m.predict_proba(train[X])\n",
-    "\n",
-    "m0.fit(train.query(f\"{T}==0\")[X], train.query(f\"{T}==0\")[y],\n",
-    "       sample_weight=1/ps_m.predict_proba(train.query(f\"{T}==0\")[X])[:, 0])\n",
-    "\n",
-    "m1.fit(train.query(f\"{T}==1\")[X], train.query(f\"{T}==1\")[y],\n",
-    "       sample_weight=1/ps_m.predict_proba(train.query(f\"{T}==1\")[X])[:, 1])\n",
-=======
     "m0.fit(train.query(f\"{T}==0\")[X], train.query(f\"{T}==0\")[y])\n",
     "m1.fit(train.query(f\"{T}==1\")[X], train.query(f\"{T}==1\")[y])\n",
->>>>>>> update chapter 21 with the newest version from original author
     "\n",
     "# estimate the CATE\n",
     "t_learner_cate_train = m1.predict(train[X]) - m0.predict(train[X])\n",
@@ -596,9 +583,9 @@
  "metadata": {
   "celltoolbar": "Tags",
   "kernelspec": {
-   "display_name": "Python 3",
+   "display_name": "Python [conda env:base] *",
    "language": "python",
-   "name": "python3"
+   "name": "conda-base-py"
   },
   "language_info": {
    "codemirror_mode": {
@@ -610,11 +597,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-<<<<<<< e022085c519423acf68e0d4c26b60d477788305d
-   "version": "3.8.5"
-=======
-   "version": "3.7.15"
->>>>>>> update chapter 21 with the newest version from original author
+   "version": "3.12.3"
   }
  },
  "nbformat": 4,