Tear variables in an equation

In some systems of equations, tearing a variable is a way of simplifying problems that need to be solved by reducing the block size of the equation set. The solver then solves the smaller blocks separately, updates the tear variable by substituting the new value, and iterating until a solution is found; for example, you may want to tear the friction factor in a pipe model so that equations, such as the complicated Colebrook equation, can be solved separately from the rest of the pipe equations. Good candidates for tearing are variables with values that are not expected to change from iteration to iteration.

By adding the tear function fx = tear(f) to an equation, you can identify a specific variable to tear.

Attempting the following results in an error:

• Tearing a derivative, such as dXdT

• Tearing a variable that appears inside a der operator (also known as a state variable)

• Tearing a variable set to a constant value, such as tear(x) = 1