Tutorial: Restore USE_MYMATH in place of MY_MATH

In commit 80f5d28813 (Tutorial: Update step 2 style, 2022-07-25,
v3.25.0-rc1~226^2) we replaced some uses of `USE_MYMATH` with `MY_MATH`.
Restore the former name for consistency with the rest of the tutorial.

Help/guide/tutorial/Adding a Library.rst

@@ -236,11 +236,12 @@ Getting Started
 Start with the resulting files from Exercise 1. Complete ``TODO 7`` through
 ``TODO 13``.
 
-First create a variable ``MY_MATH`` using the :command:`option` command
+First create a variable ``USE_MYMATH`` using the :command:`option` command
 in the top-level ``CMakeLists.txt`` file. In that same file, use that option
 to determine whether to build and use the ``MathFunctions`` library.
 
-Then, update ``tutorial.cxx`` and ``TutorialConfig.h.in`` to use ``MY_MATH``.
+Then, update ``tutorial.cxx`` and ``TutorialConfig.h.in`` to use
+``USE_MYMATH``.
 
 Build and Run
 -------------
@@ -314,9 +315,9 @@ Next, create an :command:`if` statement which checks the value of
 :command:`add_subdirectory` command from Exercise 1 with the additional
 :command:`list` commands.
 
-When ``MY_MATH`` is ``ON``, the lists will be generated and will be added to
-our project. When ``MY_MATH`` is ``OFF``, the lists stay empty. With this
-strategy, we allow users to toggle ``MY_MATH`` to manipulate what library is
+When ``USE_MYMATH`` is ``ON``, the lists will be generated and will be added to
+our project. When ``USE_MYMATH`` is ``OFF``, the lists stay empty. With this
+strategy, we allow users to toggle ``USE_MYMATH`` to manipulate what library is
 used in the build.
 
 The top-level CMakeLists.txt file will now look like the following:
@@ -380,7 +381,7 @@ will cover the modern approach in the Step 3 of the tutorial.
 
 The corresponding changes to the source code are fairly straightforward.
 First, in ``tutorial.cxx``, we include the ``MathFunctions.h`` header if
-``MY_MATH`` is defined.
+``USE_MYMATH`` is defined.
 
 .. raw:: html
 

Help/guide/tutorial/Step2/CMakeLists.txt

@@ -7,7 +7,7 @@ project(Tutorial VERSION 1.0)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED True)
 
-# TODO 7: Create a variable MY_MATH using option and set default to ON
+# TODO 7: Create a variable USE_MYMATH using option and set default to ON
 
 # configure a header file to pass some of the CMake settings
 # to the source code

Help/guide/tutorial/Step2/TutorialConfig.h.in

@@ -2,4 +2,4 @@
 #define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
 #define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
 
-// TODO 13: use cmakedefine to define MY_MATH
+// TODO 13: use cmakedefine to define USE_MYMATH

Help/guide/tutorial/Step2/tutorial.cxx

@@ -5,7 +5,7 @@
 
 #include "TutorialConfig.h"
 
-// TODO 11: Only include MathFunctions if MY_MATH is defined
+// TODO 11: Only include MathFunctions if USE_MYMATH is defined
 
 // TODO 5: Include MathFunctions.h
 
@@ -22,7 +22,7 @@ int main(int argc, char* argv[])
   // convert input to double
   const double inputValue = std::stod(argv[1]);
 
-  // TODO 12: Use mysqrt if MY_MATH is defined and sqrt otherwise
+  // TODO 12: Use mysqrt if USE_MYMATH is defined and sqrt otherwise
 
   // TODO 6: Replace sqrt with mysqrt