Modeling Tools for Environmental Engineers and Scientists

Currently available software packages suitable for authoring computerbasedmodels can be categorized into three distinct types: spreadsheet-basedapplications, equation solver-based packages, and dynamic simulation-basedpackages. Examples of packages falling into the three categories that areselected for illustration in this book are summarized in Appendix 7.1. In thischapter, some of the salient features of these example packages are outlinedand illustrated by applying them in modeling the same problem.7.2 SPREADSHEET-BASED SOFTWARESpreadsheet-based software such as Excel ® , Quattro ® Pro 7 , and Lotus ®8 ,have been available for such a long time that their features and capabilitiesare almost identical. Even though spreadsheets were originally designed aselectronic accounting books for financial analysis, they have evolved intopowerful mathematical tools and have been successfully adapted by modelersto simulate a wide range of scientific and engineering phenomena. In a way,spreadsheet applications are to numbers what word processors are to text.A worksheet in a spreadsheet application takes a tabular format, consistingof columns, designated by alphabets, and rows, designated by numerals. Theintersection of any column (for example, column P) with any row (for example,row 6) forms a cell, identified by its column heading and row number asP6 in this example. Users can click inside any cell and enter text, numericconstants or variables, built-in functions or logical expressions, or customequations, all of which in turn can use or refer to constants, variables, or evenfunctions and custom equations, contained in other cells. Custom equationscan be embedded in the cells by typing them directly on the screen using standardmathematical notations; the terms in the equations can refer to cells that,in turn, contain the constants, variables, functions, or other custom equations.Links between the cells are “live” in that any change entered into a cell willinstantly update the values of all the cells that depend on that cell as well asplots generated from those cells.Spreadsheets feature a wide range of built-in mathematical, statistical, andlogical functions that users can enter into cells using standard mathematicalnotations with minimal syntax. They also contain built-in, menu-driven routinesfor storing, formatting, and sorting data; plotting graphs; performing trialsand solutions; data analysis and curve fitting; exporting/importing data,etc. In addition, they also include an English-like scripting language thatadvanced users can adapt to write special purpose functions called “macros”7 Quattro ® Pro is a registered trademark of Corel Corporation. All rights reserved.8 Lotus ® is a registered trademark of Lotus Development Corporation. All rights reserved.© 2002 by CRC Press LLC