Neqsim Optimization And Doe

NeqSim Process Optimization & DoE Skill

NeqSim ships ~30 production-grade optimization classes. Do not reinvent optimizers in Python — use what exists, then wrap it. This skill is the discoverability layer that maps engineering problems to the right class.

Decision Tree — Which Optimizer

Need to OPTIMIZE something on a flowsheet?
│
├── ML / agentic closed loop (string addresses, never-throw JSON, replayable trajectory)?
│   → auto.newOptimizer()  (AgenticProcessOptimizer — bounded Nelder-Mead on top of evaluate())
│
├── Maximize THROUGHPUT for given P_in / P_out, with equipment constraints?
│   → ProcessOptimizationEngine.findMaximumThroughput(...)
│
├── Single decision variable, custom objective, monotonic feasibility?
│   → ProductionOptimizer + OptimizationConfig(SearchMode.BINARY_FEASIBILITY)
│
├── Single var, NON-monotonic / unimodal score?
│   → ProductionOptimizer + SearchMode.GOLDEN_SECTION_SCORE
│
├── 2–10 vars, no gradients, smooth-ish?
│   → ProductionOptimizer + SearchMode.NELDER_MEAD_SCORE
│
├── Non-convex, multiple local optima, global search?
│   → ProductionOptimizer + SearchMode.PARTICLE_SWARM_SCORE
│
├── Constrained NLP (equality + inequality + bounds), gradients OK to FD?
│   → SQPoptimizer (BFGS + active-set QP + L1 merit)
│
├── 2–4 competing objectives → Pareto front?
│   → MultiObjectiveOptimizer.optimizeWeightedSum(...) or .optimizeEpsilonConstraint(...)
│   then front.findKneePoint()
│
├── DoE / parameter sweep / scenario screening?
│   → BatchStudy.builder(base).vary(...).vary(...).addObjective(...).parallelism(8).build().run()
│
├── Uncertainty quantification, P10/P50/P90, tornado?
│   → MonteCarloSimulator (triangular sampling + tornado)
│
├── Calibrate parameters to plant/lab data?
│   → BatchParameterEstimator (LM-based) — see `neqsim-model-calibration-...`
│
├── PVT / EOS regression to experiments?
│   → LevenbergMarquardt + appropriate *Function (CME, CVD, density, etc.)
│
├── External optimizer (SciPy, NLopt, Pyomo, GA, BoTorch)?
│   → ProcessSimulationEvaluator — black-box evaluate(double[] x) bridge
│
├── Compressor specifically?
│   → CompressorOptimizationHelper
│
├── Lift curves / VFP tables for reservoir simulation?
│   → FlowRateOptimizer + LiftCurveGenerator + EclipseVFPExporter
│
└── Auto-size equipment + apply constraints + optimize, fluent API?
    → DesignOptimizer.forProcess(p).autoSizeEquipment(1.2)
        .applyDefaultConstraints().setObjective(...).optimize()

Capability Matrix

Pattern 1 — Maximize Throughput with Equipment Constraints

import neqsim.process.util.optimizer.ProcessOptimizationEngine;
import neqsim.process.util.optimizer.ProcessOptimizationEngine.SearchAlgorithm;

ProcessOptimizationEngine engine = new ProcessOptimizationEngine(processSystem);
engine.setSearchAlgorithm(SearchAlgorithm.GOLDEN_SECTION);
engine.setFeedStreamName("feed");
engine.setOutletStreamName("export");

OptimizationResult r = engine.findMaximumThroughput(
    50.0,    // inlet pressure (bara)
    10.0,    // outlet pressure (bara)
    1000.0,  // min flow (kg/hr)
    100000.0 // max flow (kg/hr)
);
System.out.println("Max flow: "  + r.getOptimalValue() + " kg/hr");
System.out.println("Bottleneck: " + r.getBottleneck());

Pattern 2 — Custom Objective with ProductionOptimizer

import neqsim.process.util.optimizer.ProductionOptimizer;
import neqsim.process.util.optimizer.ProductionOptimizer.*;
import neqsim.process.util.optimizer.ObjectiveFunction;
import neqsim.process.equipment.compressor.Compressor;

ProductionOptimizer optimizer = new ProductionOptimizer();

OptimizationConfig config = new OptimizationConfig(50000.0, 200000.0)
    .tolerance(100.0)
    .searchMode(SearchMode.GOLDEN_SECTION_SCORE)
    .maxIterations(30);

List<OptimizationObjective> objectives = Arrays.asList(
    new OptimizationObjective("power",
        proc -> ((Compressor) proc.getUnit("comp")).getPower("kW"),
        1.0, ObjectiveType.MINIMIZE));

OptimizationResult result = optimizer.optimize(process, feed, config, objectives, null);

Pattern 3 — Constrained NLP with SQPoptimizer

import neqsim.process.util.optimizer.SQPoptimizer;

SQPoptimizer sqp = new SQPoptimizer();
sqp.setObjectiveFunction(x -> -computeNPV(x, process));   // SQP minimizes
sqp.addEqualityConstraint(x -> massBalanceResidual(x));
sqp.addInequalityConstraint(x -> 200.0 - x[0]);           // P_out <= 200 bar
sqp.addInequalityConstraint(x -> x[1] - 0.05);            // surge margin >= 5%
sqp.setVariableBounds(
    new double[] {50.0,  0.0},        // lower
    new double[] {250.0, 1.0});       // upper
sqp.setInitialPoint(new double[] {120.0, 0.5});
sqp.setMaxIterations(80);

SQPoptimizer.OptimizationResult r = sqp.solve();
double[] xStar  = r.getOptimalPoint();
double   fStar  = r.getOptimalValue();
boolean  ok     = r.isConverged();

SQP rules of thumb:

• Always set tight, physically meaningful bounds — SQP is fragile without them.
• Scale variables to ~ unit magnitude (use x_scaled = (x - x_low) / (x_up - x_low) if needed).
• For ≤ 20 decision variables FD gradients are fine; provide analytical when available.
• If SQP fails to converge, escalate to Particle Swarm to find a good starting point, then re-run SQP from there.

Pattern 4 — Pareto Multi-Objective

import neqsim.process.util.optimizer.MultiObjectiveOptimizer;
import neqsim.process.util.optimizer.StandardObjective;
import neqsim.process.util.optimizer.ParetoFront;
import neqsim.process.util.optimizer.ParetoSolution;

List<ObjectiveFunction> objs = Arrays.asList(
    StandardObjective.MAXIMIZE_THROUGHPUT,
    StandardObjective.MINIMIZE_POWER);

MultiObjectiveOptimizer moo = new MultiObjectiveOptimizer();
ParetoFront front = moo.optimizeWeightedSum(process, feed, objs, baseConfig, 20);
ParetoSolution knee = front.findKneePoint();   // best trade-off

front.toCsv("pareto.csv");

Pattern 5 — DoE / Batch Sweep

import neqsim.process.util.optimizer.BatchStudy;
import neqsim.process.util.optimizer.BatchStudy.Objective;

BatchStudy study = BatchStudy.builder(baseCase)
    .vary("heater.duty",        1.0e6, 5.0e6, 5)   // 5 levels
    .vary("compressor.pressure", 30.0, 80.0, 6)    // 6 levels
    .addObjective("power",      Objective.MINIMIZE)
    .addObjective("throughput", Objective.MAXIMIZE)
    .parallelism(8)
    .build();

BatchStudyResult result = study.run();   // 30 cases run in parallel
result.exportToCSV("batch.csv");
System.out.println("Best on power:      " + result.getBestCase("power"));
System.out.println("Best on throughput: " + result.getBestCase("throughput"));

Pattern 6 — Monte Carlo Uncertainty + Tornado

import neqsim.process.util.optimizer.MonteCarloSimulator;

MonteCarloSimulator mc = new MonteCarloSimulator(process, 200);
mc.addTriangularParameter("Gas Price",   0.8,  1.5,  2.5,
    (p, v) -> setGasPriceOnProcess(p, v));
mc.addTriangularParameter("CAPEX mult.", 0.85, 1.0,  1.4,
    (p, v) -> setCapexMultiplier(p, v));
mc.addTriangularParameter("Recovery",    0.45, 0.57, 0.66,
    (p, v) -> setRecoveryFactor(p, v));
mc.setOutputExtractor("NPV (MNOK)", p -> calculateNPV(p));

MonteCarloResult result = mc.run();
System.out.println("P10="  + result.getP10());
System.out.println("P50="  + result.getP50());
System.out.println("P90="  + result.getP90());
System.out.println("P(NPV<0) = " + result.getProbabilityNegative());

// Tornado — sweep each param low→high holding others at base
result.getTornadoData().forEach((name, swing) ->
    System.out.println(name + ": swing=" + swing));

This is the mandatory pattern for the uncertainty + risk notebook in the 3-step task workflow (see AGENTS.md Step 2 requirements).

Pattern 7 — Bridge to SciPy / Pyomo / NLopt / BoTorch (Python)

from neqsim import jneqsim
from scipy.optimize import minimize, differential_evolution
import numpy as np

ev = jneqsim.process.util.optimizer.ProcessSimulationEvaluator(process)
ev.addParameter("feed",      "flowRate", 1000.0, 100000.0, "kg/hr")
ev.addParameter("comp",      "outletPressure", 50.0, 200.0, "bara")
ev.addObjective("power",     lambda p: p.getUnit("comp").getPower("kW"))
ev.addConstraint("surge",    lambda p: p.getUnit("comp").getSurgeMargin(), 0.10, 1.0)

bounds = list(ev.getBoundsAsList())

def objective(x):
    r = ev.evaluate(x)
    return float(r.getObjectives()[0])

def constraint(x):
    return list(ev.evaluate(x).getConstraintMargins())

# SciPy SLSQP
res = minimize(objective, x0=[50000, 100], bounds=bounds,
               constraints={"type": "ineq", "fun": constraint},
               method="SLSQP")

# Or differential evolution for global
res_global = differential_evolution(objective, bounds, seed=42, maxiter=50)

The same evaluator works with NLopt, Pyomo + IPOPT, DEAP (GA), scikit-optimize / BoTorch (Bayesian), or any optimizer that consumes a black-box f: R^n → R.

Pattern 8 — Auto-size + Optimize Fluent API

import neqsim.process.design.DesignOptimizer;
import neqsim.process.design.DesignOptimizer.ObjectiveType;
import neqsim.process.design.DesignResult;

DesignResult result = DesignOptimizer.forProcess(process)
    .autoSizeEquipment(1.2)            // 20% over-sizing margin
    .applyDefaultConstraints()         // pulls 18 capacity strategies
    .setObjective(ObjectiveType.MAXIMIZE_PRODUCTION)
    .optimize();

ProcessSystem optimized = result.getProcess();
result.getOptimizedFlowRates().forEach((s, q) ->
    System.out.println(s + " → " + q + " kg/hr"));

Pattern 9 — YAML Spec for Reproducibility

# optimization_spec.yaml
search:
  algorithm: GOLDEN_SECTION_SCORE
  bounds:    [50000.0, 200000.0]
  tolerance: 100.0
  maxIterations: 30
objectives:
  - name: power
    type: MINIMIZE
    weight: 1.0
constraints:
  - name: surge
    min:  0.10
    max:  1.0
    severity: HARD

import neqsim.process.util.optimizer.ProductionOptimizationSpecLoader;
ProductionOptimizationSpecLoader loader = new ProductionOptimizationSpecLoader();
OptimizationConfig cfg = loader.fromYaml("optimization_spec.yaml");

This is the canonical way to make optimization runs reproducible across notebooks, tasks, and reports.

Pattern 10 — Sensitivity Analysis Standalone

import neqsim.process.util.optimizer.SensitivityAnalysis;
import neqsim.process.util.optimizer.ProcessConstraintEvaluator;

ProcessConstraintEvaluator ev = new ProcessConstraintEvaluator(process);
ev.setCacheTTLMillis(30_000);

Map<String, Double> sens = ev.calculateFlowSensitivities(5000.0, "kg/hr");
double maxFeasibleFlow = ev.estimateMaxFlow(5000.0, "kg/hr");
String bottleneck      = ev.evaluate().getBottleneckEquipment();

Common Mistakes

Compressor control mode (choose before optimizing a charted machine)

The compressor mode decides whether speed or discharge pressure is a decision variable — get this wrong and the optimizer optimizes the wrong thing:

• Solve-speed (setOutletPressure(P) + setUseCompressorChart(True) + setSolveSpeed(True)): discharge pressure is fixed, NeqSim back-solves the speed; power and surge margin are outputs. Use when the discharge feeds a fixed pressure boundary (export pipeline, level-controlled process pressure) — e.g. max-throughput / RVP / dew-point studies. Optimize over feed rate, temperatures, routing; read power/surge/gas-load as constraints.
• Predictive (setSpeed(rpm) + setUseCompressorChart(True) + setSolveSpeed(False), no pinned outlet P): shaft speed is the input, the chart computes discharge pressure, head and power. Use when speed is your decision variable (min-power at a required export pressure) or for surge / turndown sweeps. Making a whole recycle flowsheet predictive needs the interior setOutletPressure calls dropped and a pressure-node/recycle pass to settle mixer pressures — gate it behind a PREDICTIVE_PRESSURE toggle.

See neqsim-agentic-process-optimization (§5) and neqsim-compressor-antisurge-recycle for the full pattern.

Validation Checklist

Before declaring an optimization study complete:

• Bounds on every decision variable, with units in comments
• At least two starting points tried (or PSO + SQP refinement) for non-convex problems
• Constraint violations reported in OptimizationResult.getConstraintViolations()
• Sensitivity analysis around the optimum (SensitivityAnalysis.calculate())
• Monte Carlo for the most uncertain parameters with P10/P50/P90 reported
• YAML spec saved alongside results for reproducibility
• Results written to results.json under key_results and optimization keys
• If SciPy/Pyomo used externally, the script and the bridge config saved to the task folder

Genuine Gaps (do not claim these exist)

These are NOT in NeqSim today. If a task needs them, escalate (don't fabricate):

• Bayesian optimization (Gaussian Process / Kriging surrogate, acquisition functions). Workaround: use BoTorch or scikit-optimize externally via ProcessSimulationEvaluator.
• MINLP / superstructure synthesis (true integer decision variables with branch-and-bound). Workaround: enumerate integer combinations and run continuous optimization within each.
• Interior-point NLP for very large problems (> 100 vars). SQPoptimizer is fine up to ~ 100; beyond that bridge to Pyomo + IPOPT via ProcessSimulationEvaluator.
• Latin Hypercube / Sobol / Morris sampling in BatchStudy. Today only full-factorial; for LHS use scipy's qmc module externally and feed via ProcessSimulationEvaluator.
• Robust / scenario optimization (two-stage stochastic, CVaR). Currently approximated via Monte Carlo + post-hoc filtering.
• Algorithmic differentiation of the EOS Jacobian for cubic equations. FugacityJacobian exists but is not piped into optimizers as analytical gradients.

See Also

• neqsim-production-optimization — reservoir-level production decline, gas-lift allocation, network optimization (different scope)
• neqsim-model-calibration-and-data-reconciliation — BatchParameterEstimator for plant-data tuning
• neqsim-eos-regression — LevenbergMarquardt for PVT/EOS parameter fitting
• neqsim-notebook-patterns — how to embed optimization runs in task notebooks
• neqsim-professional-reporting — optimization schema in results.json
• Documentation: docs/process/optimization/OPTIMIZATION_OVERVIEW.md and 12 sibling files