OjAlgo Source: en.wikipedia.org/wiki/OjAlgo

oj! Algorithms or ojAlgo, is an open source Java library for mathematics,^[1][2] linear algebra and optimisation. It was first released in 2003^[3] and is 100% pure Java source code and free from external dependencies. Its feature set make it particularly suitable for use within the financial domain.

• Linear algebra in Java
  • "high performance" multi-threaded feature-complete linear algebra package.
• Optimisation (mathematical programming) including LP, QP and MIP solvers.
• Finance related code (certainly usable in other areas as well):
  • Extensive set of tools to work with time series - CalendarDateSeries, CoordinationSet & PrimitiveTimeSeries.
  • Random numbers and stochastic processes - even multi-dimensional such - and the ability to drive these to do things like Monte Carlo simulations.
  • A collection of Modern Portfolio Theory related classes - FinancePortfolio and its subclasses the Markowitz and Black-Litterman model implementations.
  • Ability to download data from Yahoo Finance and Google Finance.

It requires Java 8 since version v38. As of version 44.0, the finance specific code has been moved to its own project/module named ojAlgo-finance.^[3]

Example of singular value decomposition:

SingularValue<Double> svd = SingularValueDecomposition.make(matA);
svd.compute(matA);

MatrixStore<Double> U = svd.getQ1();
MatrixStore<Double> S = svd.getD();
MatrixStore<Double> V = svd.getQ2();

Example of matrix multiplication:

PrimitiveDenseStore result = FACTORY.makeZero(matA.getRowDim(), matB.getColDim());
result.fillByMultiplying(matA, matB);