Algorithms, variables, and control flow

An algorithm is a finite sequence of unambiguous steps that solves a problem. In physics, algorithms automate calculations from numerical integration to Monte Carlo simulations.

Variables and assignment

mass = 5.0        # kilograms
velocity = 3.0    # m/s
kinetic_energy = 0.5 * mass * velocity**2

A variable stores a value in RAM (main memory) and can be updated at any time.

Control flow structures

Conditional — Execute code only when a condition is true:

if temperature > 100:
    print("Boiling!")
elif temperature > 0:
    print("Liquid")
else:
    print("Frozen")

Loop — Repeat a block of code:

# Euler method: simple numerical integration
x, v, dt = 0.0, 10.0, 0.01
for step in range(1000):
    x += v * dt
    v += -9.8 * dt   # gravity

Key hardware context

• The processor (CPU) executes instructions one at a time (or in parallel on multiple cores).
• Main memory (RAM) holds data during execution — fast but volatile.
• Secondary storage (SSD/HDD) persists data after power-off.

Tip: Always initialise variables before using them. An uninitialised variable is the most common source of bugs in scientific code.

Common pitfall: The computer does exactly what the code says, never what you meant. Off-by-one boundaries in loops and conditions are where the gap between intention and instruction bites hardest.