diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000000000000000000000000000000000000..acc9ad2ac4f09e12da41ea4890d47b0f32ca65e1
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+build
+.cache
+docs/mkdocs/site
+**/__pycache__
+tags
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a7be301af191142c33e9c6147a0e1cde17e8ad93..bdee665477eed566e85935169e8bcfca2a1f902d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,7 +13,7 @@
 #=============================================================================
 
 project                     (DIY)
-cmake_minimum_required      (VERSION 3.9)
+cmake_minimum_required      (VERSION 3.15)
 
 list (APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake)