`QuantityUtil#isEquivalentRel` does not consider zero values

[sebastian-peter]

In order to calculate the relative difference between a and b, the subtractive difference is divided by a. This means though that if a has a 0 value, the result is NaN or Infinity.

PowerSystemUtils/src/main/java/edu/ie3/util/quantities/QuantityUtil.java

Lines 143 to 150 in ff7e4da

	public static <Q extends Quantity<Q>> boolean isEquivalentRel(
	Quantity<Q> a, Quantity<Q> b, double relQuantityTolerance) {
	double aVal = a.getValue().doubleValue();
	double bVal = b.to(a.getUnit()).getValue().doubleValue();
	return (Math.abs(aVal - bVal) / Math.abs(aVal)) <= relQuantityTolerance;
	}

[sebastian-peter]

Possible solution: If a = 0, then result depends on b. If b = 0, relative difference is 0. If b is not 0, then relative difference is 1.