AbstractVector implements Vector, LengthCachingVector { @Override public double getDistanceSquared(Vector that) { if (size != that.size()) { throw new CardinalityException(size, that.size()); } double thisLength = getLengthSquared(); double thatLength = that.getLengthSquared(); double dot = dot(that); double distanceEstimate = thisLength + thatLength - 2 * dot; if (distanceEstimate > 1.0e-3 * (thisLength + thatLength)) { return Math.max(distanceEstimate, 0); } else { return aggregate(that, Functions.PLUS, Functions.MINUS_SQUARED); } } protected  AbstractVector(int size); @Override Iterable<Element> all(); @Override Iterable<Element> nonZeroes(); @Override double aggregate(DoubleDoubleFunction aggregator, DoubleFunction map); @Override double aggregate(Vector other, DoubleDoubleFunction aggregator, DoubleDoubleFunction combiner); @Override Vector viewPart(int offset, int length); @SuppressWarnings("CloneDoesntDeclareCloneNotSupportedException") @Override Vector clone(); @Override Vector divide(double x); @Override double dot(Vector x); @Override double get(int index); @Override Element getElement(int index); @Override Vector normalize(); @Override Vector normalize(double power); @Override Vector logNormalize(); @Override Vector logNormalize(double power); Vector logNormalize(double power, double normLength); @Override double norm(double power); @Override double getLengthSquared(); @Override void invalidateCachedLength(); @Override double getDistanceSquared(Vector that); @Override double maxValue(); @Override int maxValueIndex(); @Override double minValue(); @Override int minValueIndex(); @Override Vector plus(double x); @Override Vector plus(Vector that); @Override Vector minus(Vector that); @Override void set(int index, double value); @Override void incrementQuick(int index, double increment); @Override Vector times(double x); @Override Vector times(Vector that); @Override double zSum(); @Override int getNumNonZeroElements(); @Override Vector assign(double value); @Override Vector assign(double[] values); @Override Vector assign(Vector other); @Override Vector assign(DoubleDoubleFunction f, double y); @Override Vector assign(DoubleFunction f); @Override Vector assign(Vector other, DoubleDoubleFunction function); @Override Matrix cross(Vector other); @Override final int size(); @Override String asFormatString(); @Override int hashCode(); @Override boolean equals(Object o); @Override String toString(); String toString(String[] dictionary); String sparseVectorToString();  }
@Test public void testGetDistanceSquared() { Vector other = new RandomAccessSparseVector(test.size()); other.set(1, -2); other.set(2, -5); other.set(3, -9); other.set(4, 1); double expected = test.minus(other).getLengthSquared(); assertTrue("a.getDistanceSquared(b) != a.minus(b).getLengthSquared", Math.abs(expected - test.getDistanceSquared(other)) < 10.0E-7); }