public double error(final Tree<? extends Op<T>, ?> program) {
		final Result<T> result = _sampling.eval(program);
		return result != null
			? _error.apply(program, result.calculated(), result.expected())
			: Double.MAX_VALUE;
	}
Calculates the actual error for the given {@code program}.

@param program the program to calculate the error value for
@return the overall error value of the program
jenetics.prog/src/main/java/io/jenetics/prog/regression/Regression.java