### Features and Highlights

Propel is an Excel template (xlsm) designed specifically for Engineers and Scientists. Propel provides a minimal set of additional functions

*missing* from Excel. Combined with traditional cell formulas, Propel empowers users to create powerful, dynamic, and encapsulated calculations, without writing any VBA!

*Write Formulas Once, Reuse Anywhere*

Compose your complex calculation in a transparent and protected manner, complete with tests and documentation. Then, tabulate results against a multitude of new values using

SOLVEWITH. Write

*less macro code* and stop

*spreading unprotected formulas* across your spreadsheets.

*Solve Equations and ODEs, Automatically*

Write your equations and

SOLVEROOTS will find the unknowns (Newton-Raphson method). Unlike Excel's Goalseek or Solver,

*results are immediately returned without any user interaction.*
Model your mechanical and electrical systems and controls using

SOLVEODE (Runga-Kutta method).

*Simplify Widget Design*

Create hundreds of functional

widgets in minutes,

*without writing any VBA or macros*. Insert widget symbols directly into cells, and query widget status with any cell formula.

### Motivation

The above was previously thought impossible in traditional Excel.

*By definition, cell functions were NOT ALLOWED to modify other cells (values or formats, even with VBA).* This restriction simplified spreadsheets, but also created fundamental problems.

- Iterative algorithms with cell functions were not possible.
*However, some of the most useful algorithms used by Engineers and Scientist require iteration.*
- "Encapsulation" of cell functions was not possible. Engineers and Scientists prefer to bundle a concept--with parameters, variables, and formulas, clearly defined, documented, and protected at one location. However, traditional spreadsheets required
unique cell inputs to have unique cell formulas, and thus naturally
*spread formulas everywhere*. Unfortunately, this leads to mistakes and large spreadsheets quickly become
*intractable*.

The Propel template overcomes Excel's restrictions using a robust callback mechanism, which seamlessly registers and executes subroutines after each calculation event.

- Iterative algorithms are now possible (SOLVEROOTS,
SOLVEODE).
- Encapsulation is now possible (SOLVEWITH).
- Explicit formatting is now possible (FORMAT,
HIDEROW).
- Nesting of callbacks is
*allowed*. For example, solve a boundary-constrained differential equation by nesting SolveWith within SolveODE within SolveRoots.
- Distributing the file to other engineers or scientists is as simple as sending the file itself. All values are always up-to-date--users are never required to run macros or external tools (Solver, Goalseek).

Because of its widespread adoption, Excel is still the de facto method of communicating data. Propel makes the experience of using Excel more productive, more consolidated, more intuitive, and more tractable.