**Harold V. McIntosh
Departamento de Aplicación de Microcomputadoras
Instituto de Ciencias, Universidad Autónoma de Puebla
Apartado Postal 461, (72000) Puebla, Puebla, México.**

**March 18, 1989
revised January 15, 2001**

Techniques used to plot contours in the package <PLOT> are described. Aside from its using traditional interpolation formulas, <PLOT> is characterized by taking pairs of triangles rather than rectangles for primitive domains, and for tracing out one entire contour before starting another, to minimize pen raising and lowering.

- Contents
- Interpolation
- The Vandermonde matrix
- Confluence
- Specialized data points
- Three-point two-dimensional approximation
- Four-point two-dimensional approximation
- Two dimensional quadratic approximation
- Change of origin, scale
- Standardized interpolation formulas
- Three dimensional linear approximation
- Three dimensional quadratic approximation
- Fitting by least squares
- The sequence of triangles
- Checklist
- Bibliography
- About this document ...