genulens, which stands for "generate microlensing", is a tool to simulate microlensing events using Monte Carlo simulation of the Galactic model developed by Koshimoto, Baba & Bennett (2021), ApJ, 917, 78. The Galactic model is optimized for the bulge direction, and it is best to be used for analyzing microlensing events in |l| < 10 deg. and |b| < 7 deg.
The code itself has been published as Koshimoto & Ranc (2021), Zenodo.4784948. Please cite the papers if you find this code useful in your research.

A simulator for stars, genstars, is also available.

The copyright of an included supplementary code, "option.cpp", belongs to Ian A. Bond and Takahiro Sumi.

• A much more efficient simulation is available thanks to a newly introduced importance sampling feature that only simulates events with parameters that are close to the input parameters. This allows most calculations to be performed 5 to 15 times faster than before.
• Although Koshimoto, Baba & Bennett (2021), ApJ, 917, 78 did not developed their Galactic model for the Galactic Central region (|b| < 1 deg.), the nuclear stellar disk (NSD) component was added to genulens due to a demand, which affects |b| < ~0.5 deg. Although it was not fitted to the data for the Galactic Central region, we have confirmed that there is no major discrepancy with the star count data by the GALACTICNUCLEUS survey (Koshimoto et al., in preparation).
• Accordingly, the position of the Galactic Center in the model was changed from (l, b) = (0, 0) to (l, b) = (-0.056, -0.046) deg., which is the position of Sgr A*.
• The directory hierarchy was also changed. The former nkoshimoto/genulens/genulens was deleted and its contents were brought under nkoshimoto/genulens/. Therefore, if you have been using a wrapper program that assumes the previous directory structure, please change it.
• I have made a significant revision on the Usage.pdf. Now it explains many options available in genulens.
• A jupyter-notebook, genulens_samples.ipynb, is added to the repository to introduce practical analysis of some events.
• genstars, a version to simulate stars rather than microlensing events, is now available here

On June 3 2021, we released version 1.1 using a random number generator from GSL (GNU Scientific Library). This is because we realized that the random number generator from the C++ standard library, which was used in v1.0, does not have very good randomness. The statistics (the median, 1 sigma, 2 sigma values) were probably OK, but the distributions were jagged compared to the GSL one with a same number of simulation. Note that this version requires that you have GSL in your environment.

First release on May 24 2021.

Please ensure that GSL (GNU Scientific Library) is installed in your environment. If you do not have GSL, please download it from the link provided on the GSL page, and install it following README or INSTALL in the downloaded directory.

You can check where you have GSL by

gsl-config --libs

If the command gsl-config does not work in the terminal, it probably means that the GSL lib is not installed, or unknown to the OS.

If you have git, you can download the package by

git clone https://github.com/nkoshimoto/genulens.git

This is recommended because that way you can track any future updates with git.

If you do not have git, you can simply download the package by clicking the green button "Code" on the upper right in the repository page, selecting "Download ZIP", and then unzipping it.

You need a C++ compiler to make using Makefile to compile the program genulens.cpp in the downloaded directory.
The default compiler is clang++, which is available in macOS.
Please replace the first uncommented line in Makefile with g++ or any other C++ compiler if you prefer.
If you are not sure if you have clang++ or g++, you can check it by

which clang++ (or g++)

If your terminal returns a full path for it, then you have the compiler.

You might also need to change the paths for GSL specified in Makefile.
There are two lines to specify paths for GSL in the file;

INCLUDE = -I/opt/local/include
LINK = -L/opt/local/lib

Please replace the path in INCLUDE with the path returned by

gsl-config --cflags

and replace the path in LINK with the path returned by

gsl-config --libs

After making sure that you specify your C++ compiler and the paths for GSL in Makefile, you can compile the program by

make

If

./genulens

returns output lines that starts from

# Output of "./genulens "

and ends with

# Nlike/N= 100000 / 100000 wtlike/wtlike_tE= 112448 / 112448 = 1.000000

you are ready to use genulens. Note that the exact numbers of the end line might depend on your environment because the calculation uses random numbers. Please make sure that the input_files/ directory is in the same directory as where you run genulens.

See Usage.pdf.
genulens_samples.ipynb is also available and you can follow some practical event analysis using genulens.