### Question:
Absolute implements Function { @Override public Matrix derivative(final Matrix m) { return derivativei(m.dup()); }  @Override Matrix apply(final Matrix m); @Override Matrix applyi(final Matrix m); @Override Matrix derivative(final Matrix m); @Override Matrix derivativei(final Matrix m);  }### Answer:
@Test public void testAbsoluteDerivative() { final Matrix derivative = FunctionFactory.getSingleInstance("abs").derivative(input); assertTrue(expectedDerivative.compare(derivative, TOLERANCE)); }