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## Code Building

Solving the Einstein Equations for black holes in any but the most simplified cases, or for the gravitational waves spawned as they form or collide, requires building advanced computer programs or codes. When run on a computer, such codes numerically solve the equations for the behavior of the objects or phenomena that the scientists want to model.

### From Theory to Computation

The first step to solving a computational problem is applying a physical theory -- in this case, Einstein's General Theory of Relativity -- and the equations that describe that theory mathematically to a chosen physical model. The model, a representation of real-world objects or events, might be comparatively simple, a crude approximation of the real world; it might be a very complex and accurate rendering of reality. The models being investigated by relativity researchers concern highly curved spacetimes in the vicinities of black holes and other compact objects.
Next, the researchers develop efficient algorithms -- computational
"recipes" for obtaining the answer to a given problem. The scientists combine these elements -- equations, model, and algorithms -- to construct a computer code, software that enables the computer to solve the equations. The code may have to be written in different ways for different kinds of computer architectures: in many cases, these architectures cannot share code with each other.

Often codes have to be customized to a given machine's specific configuration of processors. A daunting task! No wonder numerical relativists have chosen a stepwise approach in building computer models to simulate of the behavior of black holes.

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*NCSA. Last modified 9/1/95.*