Contrib/equationReader

1 What is it?

equationReader is an extension to OpenFOAM that allows you to read equations from a dictionary file, and have them evaluated at every timestep. It works for scalars and dimensionedScalars. For example:

nu          nu [0 2 -1 0 0 0 0] "1.2 + 3 * alpha^sin(pi_/6)";
aScalar     "nu / max(5, alpha)";
alpha       1.3;

2 Features

• Order of operations - it is fully compliant with the conventional order of operations to an arbitrary parenthesis depth;
• Flexible data sources - equations can use data from any dictionary, scalar, or </tt>dimensionedScalar</tt>.
• Equation dependency tracking - equations can depend on one another to an arbitrary hierarchy depth;
• Circular-reference detection - it will halt computations when a circular reference is detected;
• On-the-fly equation mapping - it will automatically perform substitution on other equations when they are needed, even if they aren't specifically called for in the solver; and
• stand-alone, passive and active modes of operation - you can choose from three different modes of operation to suit your needs.

3 How do you use it?

3.1 Equation syntax

equationReader uses conventional order of operations BEDMAS:

• Brackets (and functions);
• Exponents;
• DM - division and multiplication; and
• AS - addition and subtraction.

Basically, if you can enter equations into Excel, you already know how to do this.

• you can use any amount of whitespace you want;
• exponents are ^, for example 2^3 is 8;
• multiplication is *, for example 2*3 is 6;
• there is no implied multiplication - you must explicitly use *. For example:

2 sin(theta) INCORRECT

2 * sin(theta) CORRECT

2(3 + 4) INCORRECT

2 * (3 + 4) CORRECT

equationReader has three modes of operation:

1. stand-alone - this one works "out of the box" with all OpenFOAM applications. You can only use literal constants in your equations;
2. passive mode - if you create an equationReader object, you can give it data sources. This allows you to use variables, and equation substitution; and
3. active mode - if you also give equationReader pointers to your output variables, it can automatically update the values at every timestep.