Portfolio VaR Calculator

# Portfolio VaR Calculator

**Role relevance:** Market Risk take-home
**Estimated time:** 60 minutes
**Difficulty:** Intermediate
**Format:** Python (.py)

## What you are given
- portfolio_var_starter.py with the function signatures stubbed and a self-check harness
- positions.csv - 4 positions and their market values (11m book)
- returns.csv - 500 business days of daily returns per asset

## What you must deliver
1. Parametric VaR of the book from the covariance matrix
2. Historical VaR from the realised PnL distribution, and a comparison
3. The diversification benefit versus the standalone position VaRs
4. Component VaR per position, summing to the portfolio total

## Constraints & assumptions
99% confidence, 1-day horizon. Use the sample covariance (ddof=1) of the supplied returns. VaR is reported as a positive loss in GBP. pandas and numpy only.

## Submission note
Complete the starter file, then compare your work against the mark scheme.