dd first-time tip, to warn against doing "make".

now i think we're reasonably safe.

Author: bjacob

CMakeLists.txt

@@ -141,22 +141,28 @@ ei_testing_print_summary()
 message("")
 message("Configured Eigen ${EIGEN_VERSION_NUMBER}")
 message("You can now do the following:")
-message("-------------+-----------------------------------------------------------------")
-message("Command      |   Description")
-message("-------------+-----------------------------------------------------------------")
-message("make install | Install to ${CMAKE_INSTALL_PREFIX}")
-message("             | To change that, do:   cmake . -DCMAKE_INSTALL_PREFIX=yourpath")
-message("make         | Build the unit tests")
-message("             | Note: that's NOT needed if you just want to install Eigen!")
-message("             | Note: this takes lots of time & memory! Easy on the -j option!")
-message("make test    | Build and run the unit tests (using CTest)")
-message("make test_qr | Build a specific test, here test_qr. To run it:   test/test_qr")
-message("make debug_qr| Build a test with full debug info. To run it:   test/debug_qr")
-message("make blas    | Build BLAS library")
-message("make doc     | Generate the API documentation, requires Doxygen & LaTeX")
-message("-------------+-----------------------------------------------------------------")
-message("")
-message("There's no need to do 'make' unless you really want to build the unit tests!")
-message("")
-
-
+message("--------------+----------------------------------------------------------------")
+message("Command       |   Description")
+message("--------------+----------------------------------------------------------------")
+message("make install  | Install to ${CMAKE_INSTALL_PREFIX}")
+message("              | To change that: cmake . -DCMAKE_INSTALL_PREFIX=yourpath")
+message("make          | Build the unit tests")
+message("              | * That's not needed if you just want to install Eigen!")
+message("              | * That takes lots of memory! Easy on the -j option!")
+message("make test     | Build and run the unit tests (using CTest)")
+message("make test_qr  | Build a specific test, here test_qr. To run it: test/test_qr")
+message("make debug_qr | Build a test with full debug info. To run it: test/debug_qr")
+message("make blas     | Build BLAS library (not the same thing as Eigen)")
+message("make doc      | Generate the API documentation, requires Doxygen & LaTeX")
+message("--------------+----------------------------------------------------------------")
+
+if(NOT EIGEN_CMAKE_ALREADY_RUN)
+  unset(EIGEN_CMAKE_ALREADY_RUN CACHE) # in case it was manually set to OFF in cache
+  set(EIGEN_CMAKE_ALREADY_RUN "ON" CACHE BOOL "Set to ON if CMake has already run here.")
+  message("")
+  message("First-time tip:")
+  message("")
+  message("If you just want to install Eigen, do 'make install' right away.")
+  message("No need to do 'make' before. See INSTALL file for more details.")
+  message("")
+endif(NOT EIGEN_CMAKE_ALREADY_RUN)

INSTALL

@@ -4,7 +4,7 @@ Installation instructions for Eigen
 Explanation before starting
 ***************************
 
-It is very important to understand than Eigen consists only of header files,
+It is very important to understand that Eigen consists only of header files,
 hence there is nothing to compile before you can use it. Moreover, these
 header files do not depend on your platform, they are the same for
 everybody.
@@ -15,14 +15,14 @@ Method 1. Installing without using CMake
 
 You can use right away the headers in the Eigen/ subdirectory. In order
 to install, just copy this Eigen/ subdirectory to your favorite location.
-If you also want the unsupported features, also copy the unsupported/
-subdirectory.
+If you also want the unsupported features, copy the unsupported/
+subdirectory too.
 
 Method 2. Installing using CMake
 ********************************
 
-Let's call this directory 'source_dir'. Before starting, create another
-directory which we will call 'build_dir'.
+Let's call this directory 'source_dir' (where this INSTALL file is).
+Before starting, create another directory which we will call 'build_dir'.
 
 Do: