2024-heraklion-parallel-python/exercises/exerciseC/README.md

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# Exercise C: blending processes and threads
Objective: investigate how the number of processes and threads impacts the
speed-up time of a computation.
## First
For each of the 19 images in the folder `images/`, the `process_images.py`:
(1) decomposes the image using a singular-value decomposition (SVD), (2) removes the
largest singular value and (3) returns the reconstructed image. The script also measures
the time for the computation and saves the result in `timings/`.
You can change the number of processes and threads on a set of images by calling the function
as follows:
```python process_images.py 3 2 images/*```
The code above will use 3 processes and 2 threads to analyse everything in the folder `images/`.
**TASKS**:
0. Familiarize yourself with the code in `process_images.py`. Where is the number of
threads set in the code? Why is it set there? Where is the number of processes set
in the code?
1. Hypothesize what would be a good number of processes and threads for this exercise.
2. Try a couple combinations of processes and threads, look at the saved timings, and see if
the results match your expectations.
## Second
This folder also includes a bash script called `run_with_all_configurations.sh`.
**TASKS**:
0. Open the bash script. What does it do?
1. Execute the bash script in the terminal:
`bash run_with_all_configurations.sh`
Observe what's printed to screen. Does it match your expectations?
2. Open `plot.py` and see what it does. Run the script and view the results. Do they
match your expectations?
3. Add the image as a comment to the Pull Request you opened in Exercise A (or make a
new Pull Request if you need one).