feat(solver): add ojAlgo backend (ExpressionsBasedModel, bounds, line…

README.md

@@ -14,7 +14,8 @@ Place for licenses, java links and passings. Inspired and copied from SBSCL and
 ![Code Size](https://img.shields.io/github/languages/code-size/draeger-lab/OptSolvX.svg?style=plastic)
 ![Downloads of all releases](https://img.shields.io/github/downloads/draeger-lab/OptSolvX/total.svg?style=plastic)
 
-OptSolvX is a flexible Java library for solving linear programming (LP) problems with multiple interchangeable solver backends.  
+OptSolvX is a flexible Java library for solving linear programming (LP) problems with multiple interchangeable solver
+backends.  
 It provides a clean, test-driven API for building, comparing and extending LP solvers.  
 OptSolvX is intended for applications in mathematics, research, and systems biology.
 
@@ -29,19 +30,17 @@ OptSolvX is intended for applications in mathematics, research, and systems biol
 - Clean logging & validation (build checks, bounds, relations)
 - Easy to extend with custom backends; demo included
 
-
 ► Status
 ----------------------------
 
 - LP modeling & solving: maximize/minimize, EQ/LEQ/GEQ constraints, variable bounds, build() workflow
 - Backends: Commons Math adapter ready; ojAlgo adapter planned
 - Builds: Java 22 by default; optional Java 8 bytecode via compat8 profile (classifier jdk8)
 
-
 ► Installation
 ----------------------------
 
-Requirements: Maven ≥ 3.9, Java 22 (default). 
+Requirements: Maven ≥ 3.9, Java 22 (default).
 
 Optional: build an additional Java 8 bytecode artifact via profile compat8.
 
@@ -51,19 +50,31 @@ cd OptSolvX
 ```
 
 Default (Java 22) - installs to local Maven repo
+
 ```
 mvn clean install
 ```
 
 Optional: Java 8 bytecode JAR (classifier jdk8)
+
 ```
 mvn -P compat8 -DskipTests clean package
 ```
 
 Artifacts
+
 - target/optsolvx-<version>.jar - Java 22 (default)
 - target/optsolvx-<version>-jdk8.jar - Java 8 bytecode (compatibility)
 
+► Java Version
+----------------------------
+
+OptSolvX requires **Java 22** to build and run.  
+The build enforces this via the Maven Enforcer plugin.
+
+If a different JDK is active, the build will fail early with a clear message.  
+Optional: use the `compat8` profile to produce a Java 8 bytecode JAR.
+
 
 ► Testing
 ----------------------------
@@ -97,20 +108,23 @@ Run the built-in demo (max x + y with two constraints) using the Commons Math ba
 **From IDE:** run `org.optsolvx.solver.SolverDemo`.
 
 **From Maven (CLI):**
+
 ```bash
 mvn -q exec:java
 # If needed:
 # mvn -q -DskipTests exec:java -Dexec.mainClass=org.optsolvx.solver.SolverDemo
 ```
 
 Expected Output:
+
 ```bash
 Variable values: {x=3.0, y=0.5}
 Objective: 3.5
 Feasible:  true
 ```
 
 ***Optional debug:*** enable verbose model logging in the demo:
+
 ```java
 model.setDebug(true); // call before model.build()
 ```

pom.xml

@@ -64,6 +64,37 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>3.2.5</version>
             </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-enforcer-plugin</artifactId>
+                <version>3.5.0</version>
+
+                <!-- Enables: mvn enforcer:enforce -->
+                <configuration>
+                    <rules>
+                        <requireJavaVersion>
+                            <version>[22,23)</version>
+                            <message>
+                                OptSolvX requires JDK 22 to build. Set JAVA_HOME to 22.x or use toolchains.
+                            </message>
+                        </requireJavaVersion>
+                    </rules>
+                    <fail>true</fail>
+                </configuration>
+
+                <!-- Keeps it bound to 'validate' as well -->
+                <executions>
+                    <execution>
+                        <id>enforce-java</id>
+                        <phase>validate</phase>
+                        <goals>
+                            <goal>enforce</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
         </plugins>
     </build>
 

src/main/java/org/optsolvx/model/AbstractLPModel.java

@@ -1,8 +1,10 @@
 package org.optsolvx.model;
 
 import static java.text.MessageFormat.format;
+
 import java.util.*;
 import java.util.logging.Logger;
+
 import org.optsolvx.model.OptimizationDirection;
 
 /**
@@ -37,42 +39,38 @@ public class AbstractLPModel {
     // The optimization direction of the model (MAXIMIZE or MINIMIZE). Default ist Maximize.
     private OptimizationDirection direction = OptimizationDirection.MAXIMIZE;
 
+    // Optional per-model solver preference (e.g., "ojalgo", "commons-math", ...).
+    private String preferredSolver;
+
     // True after build() is called; no further changes allowed
     private boolean built = false;
 
     private void beforeModelChange() {
         if (built) {
             built = false;
-            if (debug) LOGGER.warning(
-                    format(
-                            "{0}: Model was changed after build(); 'built' status reset. " +
-                                    "Please call build() again before solving.",
-                            getClass().getSimpleName()
-                    )
-            );
+            if (debug)
+                LOGGER.warning(format("{0}: Model was changed after build(); 'built' status reset. " + "Please call build() again before solving.", getClass().getSimpleName()));
         }
     }
 
     /**
      * Adds a new variable to the model.
      *
-     * @param name unique name of the variable
+     * @param name  unique name of the variable
      * @param lower lower bound (inclusive)
      * @param upper upper bound (inclusive)
      * @return index of the variable in the variables list
      * @throws IllegalArgumentException if the name already exists
-     * @throws IllegalStateException if the model is already built
+     * @throws IllegalStateException    if the model is already built
      */
     public int addVariable(String name, double lower, double upper) {
         beforeModelChange();
         if (variableIndices.containsKey(name)) {
             if (debug) LOGGER.warning("Duplicate variable name: " + name);
             throw new IllegalArgumentException("Variable name already exists: " + name);
         }
-        if (debug) LOGGER.info(format(
-                "{0}: Added variable: {1} [{2,number,0.####}, {3,number,0.####}]",
-                getClass().getSimpleName(), name, lower, upper
-        ));
+        if (debug)
+            LOGGER.info(format("{0}: Added variable: {1} [{2,number,0.####}, {3,number,0.####}]", getClass().getSimpleName(), name, lower, upper));
         Variable var = new Variable(name, lower, upper);
         int idx = variables.size();
         variables.add(var);
@@ -83,24 +81,22 @@ public int addVariable(String name, double lower, double upper) {
     /**
      * Adds a new linear constraint to the model.
      *
-     * @param name unique name of the constraint
+     * @param name   unique name of the constraint
      * @param coeffs map of variable name to coefficient in the constraint
-     * @param rel type of constraint (LEQ, GEQ, EQ)
-     * @param rhs right-hand side value of the constraint
+     * @param rel    type of constraint (LEQ, GEQ, EQ)
+     * @param rhs    right-hand side value of the constraint
      * @return the new Constraint object
      * @throws IllegalArgumentException if the name already exists
-     * @throws IllegalStateException if the model is already built
+     * @throws IllegalStateException    if the model is already built
      */
     public Constraint addConstraint(String name, Map<String, Double> coeffs, Constraint.Relation rel, double rhs) {
         beforeModelChange();
         if (constraintIndices.containsKey(name)) {
             if (debug) LOGGER.warning("Duplicate constraint name: " + name);
             throw new IllegalArgumentException("Constraint name already exists: " + name);
         }
-        if (debug) LOGGER.info(format(
-                "{0}: Added constraint {1} ({2}) rhs={3, number,0.####}, vars={4}",
-                getClass().getSimpleName(), name, rel, rhs, coeffs.keySet()
-        ));
+        if (debug)
+            LOGGER.info(format("{0}: Added constraint {1} ({2}) rhs={3, number,0.####}, vars={4}", getClass().getSimpleName(), name, rel, rhs, coeffs.keySet()));
         Constraint c = new Constraint(name, coeffs, rel, rhs);
         int idx = constraints.size();
         constraints.add(c);
@@ -111,7 +107,7 @@ public Constraint addConstraint(String name, Map<String, Double> coeffs, Constra
     /**
      * Sets the objective function for the model.
      *
-     * @param coeffs map of variable name to objective coefficient
+     * @param coeffs    map of variable name to objective coefficient
      * @param direction the optimization direction (MAXIMIZE or MINIMIZE)
      * @throws IllegalStateException if the model is already built
      */
@@ -122,57 +118,72 @@ public void setObjective(Map<String, Double> coeffs, OptimizationDirection direc
         this.direction = direction;
     }
 
+    /**
+     * Returns the optional per-model solver preference, or null if not set.
+     */
+    public String getPreferredSolver() {
+        return preferredSolver;
+    }
+
+    /**
+     * Sets the optional per-model solver preference (normalized, nullable).
+     */
+    public void setPreferredSolver(String name) {
+        this.preferredSolver = (name == null ? null : name.trim());
+    }
+
     /**
      * Finalizes the model, assigns indices to variables and constraints.
      * After calling build(), no further variables or constraints can be added
      * until the model is changed again. If the model is changed after build(),
      * the 'built' flag will be reset and build() must be called again before solving.
-     * <p>
      * Logs a summary when the model is finalized.
-     * </p>
      */
     public void build() {
         if (built) return;
-        if (debug) LOGGER.info(format(
-                "{0}: Building model with {1} variables and {2} constraints.",
-                getClass().getSimpleName(), variables.size(), constraints.size()
-        ));
+        if (debug)
+            LOGGER.info(format("{0}: Building model with {1} variables and {2} constraints.", getClass().getSimpleName(), variables.size(), constraints.size()));
         built = true;
-        if (debug) LOGGER.info(format(
-                "{0}: Model finalized. No further modifications allowed.",
-                getClass().getSimpleName()
-        ));
+        if (debug)
+            LOGGER.info(format("{0}: Model finalized. No further modifications allowed.", getClass().getSimpleName()));
     }
 
     /**
      * Returns the internal list of variables.
      * Modifications to this list affect the model directly.
+     *
      * @return the variables list
      */
-    public List<Variable> getVariables() { return variables; }
+    public List<Variable> getVariables() {
+        return variables;
+    }
 
     /**
      * Returns the internal list of constraints.
      * Modifications to this list affect the model directly.
+     *
      * @return the constraint list
      */
-    public List<Constraint> getConstraints() { return constraints; }
+    public List<Constraint> getConstraints() {
+        return constraints;
+    }
 
     /**
      * Returns the variable object with the specified name.
+     *
      * @param name the variable name
      * @return the Variable object
      * @throws IllegalArgumentException if not found
      */
     public Variable getVariable(String name) {
         Integer idx = variableIndices.get(name);
         if (idx == null) throw new IllegalArgumentException("No such variable: " + name);
-            return variables.get(idx);
-
+        return variables.get(idx);
     }
 
     /**
      * Returns the constraint object with the specified name.
+     *
      * @param name the constraint name
      * @return the Constraint object
      * @throws IllegalArgumentException if not found
@@ -183,8 +194,6 @@ public Constraint getConstraint(String name) {
         return constraints.get(idx);
     }
 
-
-
     /**
      * Returns an unmodifiable map of the objective function coefficients.
      */
@@ -194,6 +203,7 @@ public Map<String, Double> getObjectiveCoefficients() {
 
     /**
      * Returns the current optimization direction (MAXIMIZE or MINIMIZE).
+     *
      * @return the optimization direction
      */
     public OptimizationDirection getDirection() {
@@ -202,13 +212,22 @@ public OptimizationDirection getDirection() {
 
     /**
      * Sets the optimization direction for this model.
+     *
      * @param direction the optimization direction (MAXIMIZE or MINIMIZE)
      */
     public void setDirection(OptimizationDirection direction) {
         beforeModelChange();
         this.direction = direction;
     }
 
+    /**
+     * Fluent builder: set optimization direction and return this.
+     */
+    public AbstractLPModel direction(OptimizationDirection dir) {
+        setDirection(dir);
+        return this;
+    }
+
     /**
      * @return true if build() has been called and the model is finalized
      */
@@ -218,6 +237,7 @@ public boolean isBuilt() {
 
     /**
      * Returns the index of a variable by its name.
+     *
      * @param name the variable name
      * @return index of the variable in the model
      * @throws IllegalArgumentException if not found
@@ -230,6 +250,7 @@ public int getVariableIndex(String name) {
 
     /**
      * Returns the index of a constraint by its name.
+     *
      * @param name the constraint name
      * @return index of the constraint in the model
      * @throws IllegalArgumentException if not found
@@ -252,8 +273,7 @@ public String toString() {
         for (Variable v : variables) sb.append("  ").append(v).append("\n");
         sb.append("Constraints:\n");
         for (Constraint c : constraints) sb.append("  ").append(c).append("\n");
-        sb.append("Objective: ").append(objectiveCoefficients)
-                .append(" direction=").append(direction).append("\n");
+        sb.append("Objective: ").append(objectiveCoefficients).append(" direction=").append(direction).append("\n");
         return sb.toString();
     }
 
@@ -262,7 +282,7 @@ public String toString() {
      * Logging is OFF by default.
      * Call setDebug(true) before model building to activate.
      * Example: model.setDebug(true);   // Logging on
-     *          model.setDebug(false);  // Logging off
+     * model.setDebug(false);  // Logging off
      *
      */
     public void setDebug(boolean debug) {