Parallel Fractals

This project generates Julia and Mandelbrot fractals. It supports both sequential execution and parallel execution using MPI for the latter.

Compilation and Execution

1️⃣ Running the Sequential Version

If you want to run the code without MPI, you need to:

• Comment out MPI-specific code in main.cpp.
• Ensure main() calls the sequential function.
• Compile and run using g++:

  g++ main.cpp -o main
  ./main
  

2️⃣ Running the MPI (Parallel) Version

To enable parallel execution, do not comment out the MPI code, and compile using mpicxx:

mpicxx -o main main.cpp

Then, run it using mpiexec:

mpiexec -n 4 ./main

The -n 4 option tells MPI to use 4 parallel processes.

3️⃣ Running on a Cluster of Machines (Distributed Execution)

If you are running this on a cluster of VMs or multiple machines:

• Create a host file (named mpi_file in this example) listing the machines:

  node1
  node2
  node3
  node4
  

Then, run the program across the machines:

mpiexec -n 4 --hostfile mpi_file ./main

If you are interested in running it on a cluster of virtual machines but don't know where to start, I highly recommend: https://mpitutorial.com/tutorials/

How MPI Splits Workload Across Machines

• If you have 4 processes (-n 4) and 4 machines, MPI will assign 1 process per machine.
• If you have 8 processes (-n 8) and 4 machines, MPI will assign 2 processes per machine.
• If there are fewer machines than processes, MPI will distribute the load accordingly.

Example:

• -n 8 with 4 machines → Each machine gets 2 processes.
• -n 16 with 4 machines → Each machine gets 4 processes.

4️⃣ Running MPI on a Single Machine

Even if you don’t have multiple machines, you can run MPI locally:

mpiexec -n 4 ./main

🔹 This will split execution into 4 separate parallel processes on your single machine.
🔹 Useful for testing before running on a cluster.

5️⃣ Increasing Image Resolution for Zooming

To improve image detail when zooming in, modify these parameters in main.cpp:

• Increase width and height:

  This makes the image sharper when zoomed in.

• Increase max_iter:

  More iterations allow for finer fractal details.

⚠️ Warning:

Higher resolutions and iterations will increase computational load

Generated image will take up more space

Notes

• You must set up MPI and passwordless SSH for multi-machine execution.
• If you're unfamiliar with the .PPM format, I highly recommend this: https://netpbm.sourceforge.net/doc/ppm.html