Where does “piecewise linear” come from?

piecewise linear (English) comes from English piecewise, from English piece, from Middle English pece, from Old French piece, from Vulgar Latin pettia, from Latin pettia, from Gaulish pettyā, from Proto-Celtic kʷezdis — piece, portion.

piecewise linear (English): Equal to a sum of finitely many linear functions, each defined on a convex polytope: said of functions between vector spaces

Definitions

  1. Equal to a sum of finitely many linear functions, each defined on a convex polytope: said of functions between vector spaces

Ancestry of “piecewise linear”, step by step

piecewise linear traces back through two separate lines of ancestry.

via English piecewise

StepLanguageWordMeaning
1EnglishpiecewiseIn terms or by means of pieces; a piece at a...
2EnglishpieceA part of a larger whole, usually in such a form...
3Middle Englishpecepiece; morsel; bit
4Old Frenchpiecepiece, bit, part; circa 1170, Chrétien de Troyes
5Vulgar Latinpettiapiece, portion
6Latinpettiapiece, portion
7Gaulishpettyā
8Proto-Celtickʷezdispiece, portion

via English linear

StepLanguageWordMeaning
1EnglishlinearHaving the form of a line; straight or roughly...
2Latinlinearisconsisting of lines, linear, lineal;...
3LatinlīneaA linen thread
4Latinlīnumflax
5Proto-Italiclīnom
6Proto-Indo-Europeanlīnomflax
Every word from Proto-Celtic kʷezdis