Invalid function

An identifier is used in the context of a function while it doesn't denote a valid function. Example:

z = sim(z) ; "sim" is not a valid function

If sim is meant to serve as a user-defined (parameter) function, put a @ sign before it. Otherwise, change its name to a valid function.

z = @sim(z)
z = sin(z)

Note: the oldz function can only be used in the final section of coloring algorithms. Otherwise, this error is raised.

See Also
Errors