**NRPy+/SENR** is a numerical relativity code package aimed at
solving the full set of Einstein's equations of general relativity
to model compact objects at about **1/100**
the cost in memory of more traditional, AMR-based numerical relativity codes,
unlocking the desktop computer as a core tool for gravitational wave
astrophysics.

**NRPy+/SENR** gains this enormous efficiency boost via a new, dynamic
reference metric formalism. The code is designed to be open-development,
human-readable, compact, OpenMP parallelized, and
easily-extensible.

**NRPy+** ("Python-based Code generation for Numerical
Relativity and Beyond") is a new open-source code generation
package, in which users may input complex tensorial expressions in
Einstein-like notation, and the Python-based code will generate
highly-optimized C code. NRPy+
uses SymPy as its computer algebra
system backend.

**SENR** ("the Simple, Efficient Numerical Relativity code") is
a fully-functional, OpenMP parallelized numerical
relativity code in C that simply incorporates the C code generated
by **NRPy+** where needed. Its uncluttered appearance and small
number of lines of code make the algorithmic underpinnings of a
numerical relativity code transparent to the user.

We are currently working to extend existing reference metric
formalisms that produce static coordinate grids, to
generate *dynamic*, bispherical-like coordinate grids. Such
grids will be useful for modeling compact binaries in a co-rotating
frame.

**New! (Updated Aug 2018)** Interactive
NRPy+ Tutorial. (Jupyter notebooks hosted by mybinder.org)

**New! (June 2018)**
SENR can do black hole binary mergers in a co-rotating frame!

## Introductory presentation on NRPy+/SENR.

# Current Status

An at-a-glance summary of the **latest** results of our ongoing
projects. **To see more updates, click the figure below
or the navigation bar above.**

## Dec 22, 2017: Released first paper on NRPy+/SENR

### Recent results (prior to the black hole binary work) are summarized in our first paper.

### Key Result from First Paper: Black Hole Spectroscopy

We performed a black hole head-on collision simulation with SENR in sinh-spherical coordinates, and compared the resulting waveform (as measured by the absolute value of the real part of the Weyl scalar \Psi_4; the vertical scale is arbitrary) from our calculation with the exponentially decaying waveform predicted by black hole perturbation theory.

Notice that we find excellent phase and amplitude agreement to
nearly **7 decades** in amplitude. The same calculation performed
on a Cartesian AMR grid at high resolution results in disagreement
after only about 3 or 4 decades, indicating the importance of using
spherical-like coordinates in the gravitational wavezone.

**Click the figure to
learn more about SENR!**

# People

**Zachariah B. Etienne** is an assistant professor of mathematics at West Virginia University.

**Ian Ruchlin** is a post doctoral research associate in the mathematics department at West Virginia University.