Version 15 (modified by anonymous, 14 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).

## Can ANUGA run in parallel on multiple computers

Yes - there is a module using MPI (via pypar) to allow ANUGA to run in Parallel. This is not part of the standard distribution on sourceforge but can be obtained directly from the ANUGA repository (https://datamining.anu.edu.au/svn/ga/anuga_core/source/anuga_parallel)

Nils Goseberg has kindly put together some instructions which are available at https://datamining.anu.edu.au/anuga/attachment/wiki/MiscellaneousQuestions/Installation%20of%20ANUGA%20parallel.doc

## How do I run a model from the 'Tsunami Inundation Models' DVD?

This is how a user should run a model from the 'Tsunami Inundation Models' DVDs. We assume that you are using Windows and will give examples for that operating system. The translation to Linux is left as an exercise for the student!

You must copy the entire contents of the DVD to a place in your filesystem. Let's assume that you want to put the data into C:\ANUGA. You would do this in a Command Prompt window:

```C:
cd \
mkdir ANUGA
xcopy /e X:\ ANUGA
```

Of course, you could just drag all files on the DVD (X:\ is assumed) to the desired target directory with Explorer.

Now you must create an environment variable ANUGADATA that points to the directory you just created:

```set ANUGADATA=C:\ANUGA
```

Doing the above in the CMD window is temporary - if you open another CMD window you will not have the ANUGADATA environment variable defined. To make the variable permanent you must set it in the Settings|Control Panel|System tool (Advanced tab).

At this point you should run the build_elevation.py script to create a set of 'combined_elevation' files ready to be used by the ANUGA system. You may have been given the combined elevation files on your DVD (if there was room), in which case you do not strictly need to run build_elevation.py at this point. However, if you change the elevation data files you must run build_elevation.py to recreate the combined elevation files.

```cd C:\ANUGA
cd project
python build_elevation.py
```

Next, you just prepare and execute the model:

```python setup_model.py
python run_model.py
```

This should all run to completion. If you do get an error from setup_model.py or run_model.py look for some explanation in the log files, which you should find somewhere under C:\ANUGA\data. Just keep drilling down from that point until you find a directory called outputs. The latest directory in outputs should contain a file called screen_error.txt with an explanation of the error at the end.