Compare the possible meanings
| Notation | Typical meaning | How to identify it |
|---|---|---|
i²=−1 | Imaginary unit | Complex numbers |
Σᵢ aᵢ | Index | Summation |
aᵢⱼ | Row or column index | Matrices and tensors |
i=1,2,…,n | Integer variable | Discrete mathematics |
Examples
- 3+4i is a complex number.
- In Σᵢ₌₁ⁿ aᵢ, i labels terms.
- A program may use i as a loop counter without complex meaning.
How to decide
Look for complex-number operations or an explicit index range before assigning a meaning.
How to verify the interpretation
Replace i with its proposed definition and check every occurrence in the expression.