lifecycle tutorial

[nathandelcid]

Added a simple tutorial showing a lightweight entry-point example for new users who want to see the standard QuEST workflow in one small file before exploring more advanced examples.

i.e., examples/tutorials/min_lifecycle_example.c shows the basic flow of a small QuEST simulation:

• initialize the QuEST environment
• create a Qureg
• initialize the register state
• apply a couple of simple operations
• report the state
• clean up the register and environment

Kept this intentionally minimal and with elaborate comments, did not modify the existing CMake configuration. If preferred, I can follow up by wiring this into the examples build system.

[TysonRayJones]

Hi Nathan,

More examples is always more better, thanks very much for this! 🎉 However, doesn't it only meaningfully differ from the existing min_example.c by only these two lines?

    applyHadamard(qureg, 0);
    applyPauliX(qureg, 1);

[nathandelcid]

The main contribution would be the comments. Maybe I can consolidate with min_example.c?

[TysonRayJones]

That sounds better, but I note that I usually shy from redundant comments, like

// Initialise QuEST
initQuESTEnv();

// Create a qureg
Qureg qureg = createQureg(25);

// Apply some operators
applyHadamard(qureg);

// Finalise the QuEST environment.
finalizeQuESTEnv();

Such comments are just visual noise when the API function describes precisely what is happening. I much prefer "why" comments, which explain the broader context, as you can see a nice example of here. Replacing the comments with just the maths doesn't seem worthwhile - it's not a HPC simulator example's job to teach the reader what the Hadamard gate does!

I think min_example.c as exists shows the user flow fine. A longer, more meaningful example (e.g. QuEST simulating some canonical quantum algorithm) might be more worthwhile!

[nathandelcid]

Right right. I mainly did it for myself whilst reading the preprint to translate notation into code. Let me dig a little deeper and see if I can cook something up.