EasyML

Assignments

Assignments look like this:

variable = expression;

These types of statements make up the bulk of the statements within the EasyML language. EasyML differs from C and Matlab in that the order of its statements don’t matter. Variables do not need to be declared before use, and therefore

a = 3;
b = a*a;

CellML is a markup language for describing, amongst other things, ionic models. Many models are published and availmable from the CellML Model Repository. However, this format can only be processed by a machine. CARPentry uses its own MarkUp Language called EasyML.

is the same as:

b = a*a;
a = 3;

A dependency tree is built up from the assignments and as a result, variables can only be assigned to once. All variables and numeric constants are floating point numbers. Right now the parser only recognizes a subset of the C math functions. If you need to add another function email us and let us know. The absolute time is available with the variable t. The variable dt is defined and given in ms, but its use is discouraged. Use diff_XXX instead of writing your own update functions if possible. This makes it easy for you to change the integration method later.

If statements

Conditional statements can be done in two ways: C ternary operators or if statements. C ternary operators look like this:

v_abs = (v > 0) ? v : -v;

However, for nested conditionals, entering equations in this format gets tedious and ugly. Instead, we advise that you use this format:

if (v > 0) {
    v_abs = v;
} else {
    v_abs = -v;
}

This is simply syntaxic sugar for the above ternary form. In general the full syntax for if statements is if () {…} elif () {…} else {…} instead of if () {…} else if () {…} else {…}. C floating point boolean operators are used in as the conditional expressions. The translator recognizes “and, &&, or, ||”.

Note that because the order of operations doesn’t matter, there are some gotchas when using if statements. In particular, these two sections of code are equivalent:

v_abs = -v;
if (v > 0) {
    v_abs = v;
}

versus

if (v > 0) {
    v_abs = v;
} else {
    v_abs = -v;
}

To understand what value a variable takes in the presence of multiple branches, you can read the code top to bottom. This should let you copy and paste code from your existing models.

However, because of this quirk, you can’t do things like this that you could do in C

A = 50*x*x+40*x+100;
if (A > 2000) {
    A = 2000;
}

This does not clamp the variable above 2000 in the way you expect, because this is equivalent to

A = (A > 2000) ?  2000 : 50*x*x+40*x+100;

which means A depends on itself, which in turn means that A will have to be a state variable. This is not what you want. Rewrite this equation to

A_factor = 50*x*x+40*x+100;
A = A_factor;
if (A_factor > 2000) {
    A = 2000;
}

Variable updates

We also have syntaxic sugar for accumulating variables. The following two codes are equivalent: CellML is a markup language for describing, amongst other things, ionic models. Many models are published and availmable from the CellML Model Repository. However, this format can only be processed by a machine. CARPentry uses its own MarkUp Language called EasyML.

Iion = 0;
Iion += INa;
Iion += Ito;

versus

Iion = 0+INa+Ito;

Markup

Markup statements change the way the code handles some variables compared to others. A markup statement takes the form:

.markup_function(optional_arguments);

The markup function is applied to the variable definition or declaration immediately preceding the markup command. Therefore,

X; .external();
Y = 3;
Z = 3; .external();

applies the .external markup to X and Z. If a markup follows an if statement, the markup applies to every variable definition or declaration enclosed in that if statement.

In order to avoid tedious repetition of markup statements, the group directive can be used:

group {
    X;
    Z = 3;
} .external();
Y = 3;

group statements can be nested, and like an if statement, a group statement collects every declared/defined variable it encloses for markup.