Fix high memory usage with DC Sensitivity Analysis and DC Woodbury Se…

…curity Analysis (#1109)

Signed-off-by: PRABAKARAN Sylvestre <sylvestre.prabakaran@rte-france.com>

src/main/java/com/powsybl/openloadflow/sa/WoodburyDcSecurityAnalysis.java

@@ -202,6 +202,7 @@ protected SecurityAnalysisResult runSimulations(LfNetwork lfNetwork, List<Propag
             cleanContingencies(lfNetwork, propagatedContingencies);
 
             double[] preContingencyStates = DcLoadFlowEngine.run(context, new DisabledNetwork(), reportNode);
+            double[] baseContingencyStates = preContingencyStates.clone();
 
             // set pre contingency angle states as state vector of equation system
             context.getEquationSystem().getStateVector().set(preContingencyStates);
@@ -238,7 +239,7 @@ protected SecurityAnalysisResult runSimulations(LfNetwork lfNetwork, List<Propag
 
                             logPostContingencyStart(lfNetwork, lfContingency);
                             Stopwatch stopwatch = Stopwatch.createStarted();
-
+                            System.arraycopy(baseContingencyStates, 0, preContingencyStates, 0, baseContingencyStates.length);
                             double[] postContingencyStates = calculatePostContingencyStatesForAContingency(context, connectivityBreakAnalysisResults.contingenciesStates(), preContingencyStates, propagatedContingency,
                                     connectivityBreakAnalysisResults.contingencyElementByBranch(), Collections.emptySet(), Collections.emptySet(), reportNode, Collections.emptySet());
                             // compute post contingency result with post contingency states

src/main/java/com/powsybl/openloadflow/sensi/DcSensitivityAnalysis.java

@@ -13,6 +13,7 @@
 import com.powsybl.iidm.network.Network;
 import com.powsybl.loadflow.LoadFlowParameters;
 import com.powsybl.math.matrix.DenseMatrix;
+import com.powsybl.math.matrix.DenseMatrixFactory;
 import com.powsybl.math.matrix.MatrixFactory;
 import com.powsybl.openloadflow.OpenLoadFlowParameters;
 import com.powsybl.openloadflow.dc.DcLoadFlowContext;
@@ -231,7 +232,6 @@ private void calculateSensitivityValuesForAContingency(DcLoadFlowContext loadFlo
             DenseMatrix postContingencyFlowStates = engine.run(newFlowStates);
             DenseMatrix postContingencyFactorStates = engine.run(newFactorStates);
             calculateSensitivityValues(factors, postContingencyFactorStates, postContingencyFlowStates, contingency, resultWriter, disabledNetwork);
-
             // write contingency status
             if (contingency.hasNoImpact()) {
                 resultWriter.writeContingencyStatus(contingency.getIndex(), SensitivityAnalysisResult.Status.NO_IMPACT);
@@ -438,13 +438,14 @@ public void analyse(Network network, List<PropagatedContingency> contingencies,
                         : Collections.emptyList();
 
                 // run DC load on pre-contingency network
-                DenseMatrix flowStates = calculateFlowStates(loadFlowContext, participatingElements, new DisabledNetwork(), reportNode);
-
+                DenseMatrix baseFlowStates = calculateFlowStates(loadFlowContext, participatingElements, new DisabledNetwork(), reportNode);
+                DenseMatrix flowStates = (DenseMatrix) baseFlowStates.copy(new DenseMatrixFactory());
                 // compute the pre-contingency factor states
-                DenseMatrix factorsStates = calculateFactorStates(loadFlowContext, factorGroups, participatingElements);
+                DenseMatrix baseFactorStates = calculateFactorStates(loadFlowContext, factorGroups, participatingElements);
+                DenseMatrix factorStates = (DenseMatrix) baseFactorStates.copy(new DenseMatrixFactory());
 
                 // calculate sensitivity values for pre-contingency network
-                calculateSensitivityValues(validFactorHolder.getFactorsForBaseNetwork(), factorsStates, flowStates, null, resultWriter, new DisabledNetwork());
+                calculateSensitivityValues(validFactorHolder.getFactorsForBaseNetwork(), factorStates, flowStates, null, resultWriter, new DisabledNetwork());
 
                 // filter contingencies without factors
                 List<PropagatedContingency> contingenciesWithFactors = new ArrayList<>();
@@ -464,23 +465,45 @@ public void analyse(Network network, List<PropagatedContingency> contingencies,
 
                 // process contingencies with no connectivity break
                 for (PropagatedContingency contingency : connectivityBreakAnalysisResults.nonBreakingConnectivityContingencies()) {
+                    matrixShallowCopy(baseFlowStates, flowStates);
+                    matrixShallowCopy(baseFactorStates, factorStates);
+
                     calculateSensitivityValuesForAContingency(loadFlowContext, lfParametersExt, validFactorHolder, factorGroups,
-                            factorsStates, connectivityBreakAnalysisResults.contingenciesStates(), flowStates, contingency,
+                            factorStates, connectivityBreakAnalysisResults.contingenciesStates(), flowStates, contingency,
                             connectivityBreakAnalysisResults.contingencyElementByBranch(), Collections.emptySet(), participatingElements, Collections.emptySet(), resultWriter, reportNode, Collections.emptySet(), false);
                 }
 
                 LOGGER.info("Processing contingencies with connectivity break");
 
                 // process contingencies with connectivity break
                 for (ConnectivityBreakAnalysis.ConnectivityAnalysisResult connectivityAnalysisResult : connectivityBreakAnalysisResults.connectivityAnalysisResults()) {
+                    matrixShallowCopy(baseFlowStates, flowStates);
+                    matrixShallowCopy(baseFactorStates, factorStates);
+
                     processContingenciesBreakingConnectivity(connectivityAnalysisResult, loadFlowContext, lfParameters, lfParametersExt,
                             validFactorHolder, factorGroups, participatingElements, connectivityBreakAnalysisResults.contingencyElementByBranch(),
-                            flowStates, factorsStates, connectivityBreakAnalysisResults.contingenciesStates(), resultWriter, reportNode);
+                            flowStates, factorStates, connectivityBreakAnalysisResults.contingenciesStates(), resultWriter, reportNode);
                 }
             }
 
             stopwatch.stop();
             LOGGER.info("DC sensitivity analysis done in {} ms", stopwatch.elapsed(TimeUnit.MILLISECONDS));
         }
     }
+
+    /**
+     * Copy all the values that are in an originalMatrix and paste it in the copyMatrix (without allocating new memory spaces)
+     * The dimensions of both matrices must be the same
+     */
+    // TODO : implement this method for DenseMatrix in powsybl-core ?
+    private static void matrixShallowCopy(DenseMatrix originalMatrix, DenseMatrix copyMatrix) {
+        if (originalMatrix.getRowCount() == copyMatrix.getRowCount() && originalMatrix.getColumnCount() == copyMatrix.getColumnCount()) {
+            for (int columnIndex = 0; columnIndex < originalMatrix.getColumnCount(); columnIndex++) {
+                for (int rowIndex = 0; rowIndex < originalMatrix.getRowCount(); rowIndex++) {
+                    copyMatrix.set(rowIndex, columnIndex, originalMatrix.get(rowIndex, columnIndex));
+                }
+            }
+        }
+    }
+
 }

src/main/java/com/powsybl/openloadflow/sensi/WoodburyEngine.java

@@ -84,12 +84,12 @@ private void setAlphas(DenseMatrix states, int columnState) {
 
     /**
      * Calculate post-contingency states values using pre-contingency states values and some flow transfer factors (alphas).
-     * @return a matrix of post-contingency voltage angle states.
+     * @return a matrix of post-contingency voltage angle states (which is the same modified pre-contingency states java object).
      */
     public DenseMatrix run(DenseMatrix preContingencyStates) {
         Objects.requireNonNull(preContingencyStates);
         // fill the post contingency matrices
-        DenseMatrix postContingencyStates = new DenseMatrix(preContingencyStates.getRowCount(), preContingencyStates.getColumnCount());
+        DenseMatrix postContingencyStates = preContingencyStates;
         for (int columnIndex = 0; columnIndex < preContingencyStates.getColumnCount(); columnIndex++) {
             setAlphas(preContingencyStates, columnIndex);
             for (int rowIndex = 0; rowIndex < preContingencyStates.getRowCount(); rowIndex++) {
@@ -106,11 +106,11 @@ public DenseMatrix run(DenseMatrix preContingencyStates) {
 
     /**
      * Calculate post-contingency states values using pre-contingency states values and some flow transfer factors (alphas).
-     * @return an array of post-contingency voltage angle states.
+     * @return an array of post-contingency voltage angle states (which is the same modified pre-contingency java object).
      */
     public double[] run(double[] preContingencyStates) {
         Objects.requireNonNull(preContingencyStates);
-        double[] postContingencyStates = new double[preContingencyStates.length];
+        double[] postContingencyStates = preContingencyStates;
         setAlphas(new DenseMatrix(preContingencyStates.length, 1, preContingencyStates), 0);
         for (int rowIndex = 0; rowIndex < preContingencyStates.length; rowIndex++) {
             double postContingencyValue = preContingencyStates[rowIndex];