Migrate the lp_solve code from C, Java to Android.

Version of lp_solve: 5.5.2.5

Few days ago, I was developing some tools for Princess Connect Re:Dive and met the problem of linear programming.

However, when I try the org.apache.commons:commons-math3 library, it shows the BAD performance as the constraints and variable increase. That's the reason why I migrate the lp_solve library from C to Android.

It's believed that lp_solve libraries give the correct answer at least **10 TIMES FASTER THAN ** org.apache.commons:commons-math3. And the accuracy has increased dramatically, compared to the former.

Before we go on, we shall check some prerequisites:

1. Android Studio
2. CMake

After that, download the latest lpsolve_android_release.zip in release page and unzip it. The directory structure is listed below

app
  - build.gradle
  - src
    - main
      - cpp
        - CMakeLists.txt
        - ...More
      - java
        - lpsolve
        - ...More
lpsolve_bin
  - lib
    - arm64-v8a
    - armeabi-v7a
    - x86
    - x86_64

The directories inside lpsolve_bin/lib contain the .so libraries for each platforms.

There are 2 different ways to lay out the lp_solve libraries.

First, build a NDK project in AS.

The file structure in directory app correspond to the real structure in ndk project of Android Studio. Then:

1. Put the files in directory app/src in the corresponding location of the ndk project. Make sure the lpsolve package is the subdirectory of app/src/main/java and the cpp dir is the subdirectory of app/src/main, or it may cause errors.
2. Modify the build.gradle in app as below:

android{
	...
	defaultConfig{
		...
		# Here define the parameters which control the cmake
        	externalNativeBuild {
            		cmake {
                		cFlags ""
                		cppFlags ""
            		}
        	}
	}
	...
	# Here is the relative path of the CMakeList.txt
    	externalNativeBuild {
        	cmake  {
			path "src/main/cpp/CMakeLists.txt"
       		}
    	}
}

1. Start an existing android project with AS.

2. Put the files in directory app/src in the corresponding location of the NDK project. Make sure the lpsolve package is the subdirectory of app/src/main/java and the cpp directory is the subdirectory of app/src/main, or it may cause errors.

3. Open the Project pane from the left side of the IDE and select the Android view.

4. Right-click on the module you would like to link to your native library, such as the app module, and select Link C++ Project with Gradle from the menu.

5. From the drop-down menu, select CMake. Then, use the field next to Project Path to specify the src/main/cpp/CMakeLists.txt script file for your external CMake project.

6. Click OK.

Above steps could be referred to Link Gradle to your native library on the website of Android Developers.

When everything is done, you could import the lpsolve package the same as what we do with Java.

And every time the .apk file is compiled and built, the lpsolve would be packed in it.

lp_solve reference guide

The MIT License

The project relies on:

• lp_solve