Added file on index_select

content/pytorch/concepts/tensor-operations/terms/index_select/index_select.md

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+---
+Title: '.index_select()'
+Description: 'Extracts specific elements from a tensor to return a new tensor.'
+Subjects:
+  - 'AI'
+  - 'Data Science'
+Tags:
+  - 'AI'
+  - 'Arrays'
+  - 'Data Structures'
+  - 'Deep Learning'
+CatalogContent:
+  - 'intro-to-py-torch-and-neural-networks'
+  - 'paths/computer-science'
+---
+
+**Index_select()** is used to extract specific elements (rows, columns) from the tensor to return a new tensor. 
+
+## Syntax
+
+```pseudo
+torch.index_select(input,dim,index,out)
+```
+
+- `input`: The input tensor
+- `dim`: The dimension to index (0 for rows, 1 for columns)
+- `index`: The 1-D tensor containing the indices to select
+- `out` (optional): The output tensor (optional)
+
+## Example
+
+The following example demonstrates the usage of `.index_select()`:
+
+```py
+import torch
+
+#Define a tensor
+ten = torch.tensor([[1, 2, 3, -8],
+                    [4, 3, 8, 0],
+                    [-1, 7, 6, 3],
+                    [5, 6, 9, 0]])
+
+indices = torch.tensor([0, 2])
+
+#Define a new tensor using index_select 
+r = torch.index_select(ten, 0, indices)
+print(r)
+
+#Define a new tensor using index_select 
+c = torch.index_select(ten, 1, indices)
+print(c)
+```
+
+```shell
+tensor([[1, 2, 3, -8],
+        [-1, 7, 6, 3]])
+tensor([[1, 4, -1, 5],
+        [3, 8, 6, 9]])
+```