Δδ
MATHEMATICS
- Change/difference: Δx.
- Kronecker delta δᵢⱼ and Dirac delta δ(·).
PROBABILITY
- Point mass can be written with δ(·) in measure theory.
- Difference between events/values (Δ).
STATISTICS
- Difference of means/effects: Δ.
- Increments in numerical optimization.
PRONUNCIATION
- Ancient Greek
- sound [d]
- Modern Greek
- δέλτα [ˈðelta] · sound [ð]
IN FORMULAS
- Δ = b² − 4acThe discriminant of a quadratic: it tells how many real roots there are.See it explained at morrisonkuhlsen.com →
- Δy / ΔxChange in y over change in x: the slope between two points.
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Note: notations vary between books/fields; these are the most common usages.