Version 3 (modified by ole, 15 years ago) (diff)

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# Miscellaneous Questions

This part of the FAQ is for questions that have no obvious place elsewhere. This is also a good place to start a question that you would like answered.

## How do I get a question answered?

The best way is to start a new question on this page. Just cut-and-paste this question/answer to somewhere below here and leave the answer part blank. Or perhaps you can discuss the question in more detail.

## Why does ANUGA get so slow when meshes are refined

Two reasons:

• With smaller triangles timesteps tend to become smaller due to the CFL condition
• The computation time per timestep grows more than linearly with the number of triangles. Here is why
```Let h be the grid size. The number of cells (triangles) N will normally be proportional to h^{-2}
The size of the timesteps will be proportional to the grid size, and so the number of timesteps is proportional to h^{-1} = N^{1/2}
So the computational cost (solution time) will be proportional to
(number of cells) x (no of timesteps) = N x N^{1/2} = N^{3/2}
log (Time) = 3/2 log( N).

So increasing the grid size from 100 cells to 1000 cells grows the computational time by 10^{3/2} (about 30).
```