use of auto differentiation for F function

src/main/java/neqsim/thermo/phase/PhaseAutoDifferentiation.java

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+package neqsim.thermo.phase;
+
+import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import neqsim.thermo.component.ComponentSrk;
+
+/**
+ * <p>
+ * PhasePCSAFT class.
+ * </p>
+ *
+ * @author Even Solbraa
+ * @version $Id: $Id
+ */
+public class PhaseAutoDifferentiation extends PhaseEos {
+  private static final long serialVersionUID = 1000;
+
+  static Logger logger = LogManager.getLogger(PhaseAutoDifferentiation.class);
+  DerivativeStructure funcToBeDifferentiated = null;
+
+  double Bll = 0.0;
+  double All = 0.0;
+
+  /**
+   * <p>
+   * Constructor for PhasePCSAFT.
+   * </p>
+   */
+  public PhaseAutoDifferentiation() {
+    super();
+    delta1 = 1.0 + Math.sqrt(2.0);
+    delta2 = 1.0 - Math.sqrt(2.0);
+    uEOS = 2;
+    wEOS = -1;
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public PhaseAutoDifferentiation clone() {
+    PhaseAutoDifferentiation clonedPhase = null;
+    try {
+      clonedPhase = (PhaseAutoDifferentiation) super.clone();
+    } catch (Exception e) {
+      logger.error("Cloning failed.", e);
+    }
+
+    return clonedPhase;
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public void addcomponent(String componentName, double moles, double molesInPhase,
+      int compNumber) {
+    super.addcomponent(molesInPhase);
+    componentArray[compNumber] =
+        new ComponentSrk(componentName, moles, molesInPhase, compNumber);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public void init(double totalNumberOfMoles, int numberOfComponents, int type, int phase,
+      double beta) {
+    Bll = calcB(this, temperature, pressure, 1);
+    All = calcA(this, temperature, pressure, 1);
+    if (type == 0) {
+      //Setting up function to be dieeferentiad
+      funcToBeDifferentiated = getFunctionStruc();
+    }
+    if (type > 0) {
+      funcToBeDifferentiated = getFunctionStruc();
+      for (int i = 0; i < numberOfComponents; i++) {
+        componentArray[i].Finit(this, temperature, pressure, totalNumberOfMoles, beta,
+            numberOfComponents, type);
+      }
+    }
+    // super.init(totalNumberOfMoles, numberOfComponents, type, phase, beta);
+  }
+
+  public DerivativeStructure getFunctionStruc(){
+    int params = 2;
+    int order = 2;
+    double tRealValue = getTemperature();
+    double vRealValue = getVolume();
+
+    double numberOfMoles = getNumberOfMolesInPhase();
+
+    DerivativeStructure tVar = new DerivativeStructure(params, order, 0, tRealValue);
+    DerivativeStructure vVar = new DerivativeStructure(params, order, 1, vRealValue);
+    //
+    DerivativeStructure BdivVstruct = vVar.pow(-1.0).multiply(Bll);
+    DerivativeStructure BdivVstruct2 =
+        tVar.createConstant(-1.0).multiply((tVar.createConstant(1.0).subtract(BdivVstruct)).log());
+
+    DerivativeStructure Dstruct =
+        tVar.createConstant(-1.0 * All / R / getB() / (delta1 - delta2)).divide(tVar);
+    DerivativeStructure Dstruct2 =
+        tVar.createConstant(1.0).add(tVar.createConstant(delta1 * Bll).divide(vVar));
+    DerivativeStructure Dstruct3 =
+        tVar.createConstant(1.0).add(tVar.createConstant(delta2 * Bll).divide(vVar));
+    DerivativeStructure Dstruct4 = Dstruct.multiply(Dstruct2.divide(Dstruct3));
+
+    DerivativeStructure Ffinal = BdivVstruct2.add(Dstruct4);
+
+    DerivativeStructure tTimesV = tVar.add(vVar.multiply(3.0));
+    return tTimesV;
+  }
+
+
+  /** {@inheritDoc} */
+  @Override
+  public double getF() {
+    return funcToBeDifferentiated.getValue();
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public double dFdV() {
+
+    return funcToBeDifferentiated.getPartialDerivative(0, 1);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public double dFdVdV() {
+     return 1.0;
+  }
+
+}

src/test/java/neqsim/thermo/phase/PhaseAutoDifferentiationTest.java

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+package neqsim.thermo.phase;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class PhaseAutoDifferentiationTest {
+
+  static PhaseAutoDifferentiation phase = null;
+  static DerivativeStructure function = null;
+
+  @BeforeAll
+  public static void setUp() {
+    phase = new PhaseAutoDifferentiation();
+    phase.addcomponent("methane", 1.0, 1.0, 0);
+    phase.setTemperature(300.0);
+    phase.setMolarVolume(100.0);
+    phase.numberOfMolesInPhase = 1.0;
+    phase.setTotalVolume(100.0);
+    phase.init(1, 1, 0, 1, 1);
+    phase.init(1, 1, 1, 1, 1);
+    function = phase.getFunctionStruc();
+
+  }
+
+  @Test
+  void testDFdV() {
+    assertEquals(3.0, function.getPartialDerivative(0, 1), 1e-6);
+  }
+
+  @Test
+  void testDFdT() {
+    assertEquals(1.0, function.getPartialDerivative(1, 0), 1e-6);
+  }
+
+  @Test
+  void testDFdVdV() {
+    assertEquals(0.0, function.getPartialDerivative(0, 2), 1e-6);
+  }
+
+  @Test
+  void testGetF() {
+    assertEquals(600.0, function.getValue(), 1e-6);
+  }
+
+
+}