Optional backend (#30)

* update readme with dependencies

* dummy to test the CI workflow

* make Sparse2D backend as optional

* update optional workflow

* make Sparse2D optional

* minor variable name change

Author: ChaitanyaChawak

README.md

@@ -6,15 +6,22 @@ Software developed at the [CosmoStat](https://www.cosmostat.org/) lab at [CEA](h
 
 ## Basic installation
 
+This package has an option to install [Sparse2D](https://github.com/CosmoStat/Sparse2D) as a backend (disabled by default). 
+
 The package can be installed with `pip` as follows.
 
 ```bash
 python -m pip install .
+```
+
+ To install the Sparse2D backend along with the package installation, run:
+```bash
+BUILD_SPARSE2D=ON python -m pip install .
 ```
 
 ### Requirements
 
-This package installs [Sparse2D](https://github.com/CosmoStat/Sparse2D) as a backend, which requires the follow dependencies.
+[Sparse2D](https://github.com/CosmoStat/Sparse2D) requires the following dependencies.
 
 - [Armadillo](https://arma.sourceforge.net/)
 - [BigMac](https://github.com/sfarrens/bigmac) (macOS only)
@@ -41,7 +48,7 @@ To install the package requirements on Ubuntu, it is recommended to use [apt](ht
 
 ```bash
 sudo apt-get update
-sudo apt-get install -y libarmadillo-dev libcfitsio-dev libfftw3-dev libgsl-dev libhealpix-cxx-dev pkg-config
+sudo apt-get install -y libarmadillo-dev libcfitsio-dev cmake libfftw3-dev libgsl-dev libhealpix-cxx-dev pkg-config build-essential 
 ```
 
 ## Docker installation

src/cxx/CMakeLists.txt

@@ -24,5 +24,13 @@ message(STATUS "Python binding install path : ${Python_EXECUTABLE}")
 get_filename_component(SPARSE2D_INSTALL_DIR ${Python_EXECUTABLE} DIRECTORY)
 message(STATUS "Binary install path : ${SPARSE2D_INSTALL_DIR}")
 
-# Build Sparse2D
-include(BuildSparse2D)
+# Build Sparse2D (optionally)
+if (DEFINED ENV{BUILD_SPARSE2D})
+    set(BUILD_SPARSE2D $ENV{BUILD_SPARSE2D})
+else()
+    set(BUILD_SPARSE2D OFF)
+endif()
+
+if (BUILD_SPARSE2D)
+    include(BuildSparse2D)
+endif()