Diaeresis

In linguistics, a diaeresis or dieresis (AE) (from Greek ???????? (diaerein), to divide) is the modification of a syllable by distinctly pronouncing one of its vowels. The diacritic mark composed of two small dots ( ¨ ) placed over a vowel to indicate this modification is also called a diaeresis. (In the case of an "i", it replaces the original dot.)

Time derivatives in mathematics

The derivative with respect to time is often represented as a dot above a variable. Two dots represents the second derivative.

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:{dot{a}} = {mathrm{d} over mathrm{d}t} a

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:{ddot{a}} = {mathrm{d} ^2 over mathrm{d} t ^2} a

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This may be contrasted with the more common notation for a derivative using a prime:

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:f'(x) = {mathrm{d} over mathrm{d}x} f(x)

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:f(x) = {mathrm{d}^2 over mathrm{d}x^2} f(x)

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