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docs/lib3x-m_replace.md

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+# m_replace
+
+It replaces the aᵢⱼ element of a matrix.
+
+**Since:** 3.3
+
+## Parameters
+
+- `m` : A matrix.
+- `i` : The i-th row.
+- `j` : The j-th column.
+- `value` : The new value.
+
+## Examples
+
+    use <matrix/m_replace.scad>
+
+    original_m = [
+        [1, 2, 3, 4],
+        [5, 6, 7, 8],
+        [9, 10, 11, 12]
+    ];
+
+    expected = [
+        [1, 2, 3, 4],
+        [5, 6, 70, 8],
+        [9, 10, 11, 12]
+    ];
+
+    actual = m_replace(original_m, 1, 2, 70);
+
+    assert(actual == expected);