Plinth

Hardware-accelerated matrix/numeric programming library for Swift.

Installation

Swift Package Manager

Simply add Plinth to your Package.swift file:

let package = Package(
    name: "Example",
    dependencies: [
        .package(url: "https://github.com/dclelland/Plinth.git", from: "2.0.0"),
    ],
    targets: [
        .target(name: "Example", dependencies: ["Plinth"])
    ]
)

Then import Plinth into your Swift files:

import Plinth

Or for full ComplexMatrix support you should also import swift-numerics, as that’s where the Complex type lives.

import Plinth
import Numerics

Todo

Implement Equality/Comparisons extension
Implement both .zeros and .ones initializers
Implement exception handling for LAPACK calls
Implement wrappers for vDSP.fill, vDSP.clear, vDSP.window, vDSP.ramp, vDSP.stereoRamp
Implement wrapper for vDSP.convolve
Revisit Eigendecomposition.sorted, is sorting the eigenvalues by real component or the magnitude preferable?
Write notes on architecture and API design
Write code examples
~~Add Cocoapods support~~ Can’t do this, swift-numerics only supports SPM. Perhaps I should make my own Complex type.

Documentation

Types

Shape

Defines the shape of a matrix using rows and columns properties.

public struct Shape {
    
    public let rows: Int
    public let columns: Int
    
}

This includes a number of convenience properties like count, length and breadth; as well as convenience initializers .row(length:), .column(length:) and .square(length:).

Matrix

Generic matrix struct with Scalar type argument and shape and elements properties. Elements are stored as a single array in row-major format.

public struct Matrix<Scalar> {
    
    public let shape: Shape
    public var elements: [Scalar]
    
}

This also includes a large number of convenience initializers and implementations of typical typeclasses such as Codable and ExpressibleByArrayLiteral.

The elements property is directly mutable but this is ideally to be avoided; matrix regularity is not enforced, except during encoding to or decoding from a serialization format.

There is a computed property state which can be used to check if the matrix is considered to be malformed:

let malformed = Matrix<Double>(
    shape: .init(rows: 2, columns: 2),
    elements: [1.0, 2.0, 3.0, 4.0, 5.0]
)

print(malformed.state)

> Malformed: Mismatched shape and elements; 2×2 != 5

ComplexMatrix

Generic complex matrix struct encapsulating two separate matrices for the real and imaginary parts.

public struct ComplexMatrix<Scalar> where Scalar: Real {
    
    public var real: Matrix<Scalar>
    public var imaginary: Matrix<Scalar>
    
}

This also includes a large number of convenience initializers and implementations of typical typeclasses such as Codable and ExpressibleByArrayLiteral.

The real and imaginary properties are also directly mutable; ComplexMatrix has its own state property which can be used to check if the parts are mismatched or malformed.

Core

Arithmetic

+ and - prefix operators and +, -, *, / infix operators.

Implements fast pointwise arithmetic for combinations of Scalar, Complex<Scalar>, Matrix<Scalar> and ComplexMatrix<Scalar>, where Scalar is Float or Double.

Conversions

Fast type conversions between the integer types UInt8, UInt16, UInt32, Int8, Int16, Int32 and the floating point types Float and Double.

Functors

Higher-order functions for shape-preserving operations on a matrix’s elements.

Includes support for complex matrix operations on DSPSplitComplex/DSPDoubleSplitComplex.

Disclaimer: These are not true functors, Swift lacks higher-kinded types…

Submatrix

Fast submatrix read/write access using a Swift subscript interface.

Uses Accelerate’s vDSP_mmov/vDSP_mmovD.

Wrappers

Wrappers over most of the basic vDSP and vForce functions in Accelerate.

Transformations

Center

Find the center point of a matrix, given a rounding rule.

Crop

Crop a matrix towards the center, given a rounding rule.

Pad

Zero-pad a matrix away from the center, given a rounding rule.

Reshape

Apply a new shape to a matrix, or reshape it as a single row or column.

This also supports both .rowMajor and .columnMajor orderings.

Shift

Apply a circular shift to a matrix.

Concatenate

Concatentate multiple matrices together, row-wise or column-wise.

Comparisons

<, <=, >, >=, ==, !== infix operators.

Pointwise comparison or equality checks, returning 0.0 for false and 1.0 for true.

Mathematics

Powers

** infix operator.

Implements fast pointwise power operations for Scalar and Matrix.

Includes special functions for taking integer powers of matrices, for use when recursive application of vDSP.multiply will be faster than vForce.pow (which is quite an expensive operation).

This also supports negative integers by applying vForce.reciprocal to the result.

Interpolation

Linear interpolate values from a given range to/from 0.0...1.0.

This is similar to C++’s std::lerp.

Statistics

Random

Generate matrices populated with random noise.

Gaussian

Generate matrices populated with Gaussian noise.

This is derived from an answer on the comp.lang.c FAQ.

Moments

Calculate central and standardized moments; convenience methods for variance, standardDeviation, skewness, and kurtosis.

Normalization

Normalize a matrix to 0.0...1.0 using its minimum() and maximum() values; or shift it so that its mean() is centered on zero.

Linear Algebra

Zeros

Generate matrices populated by zeros.

Ones

Generate matrices populated by ones.

Identity

Generate identity matrices.

Diagonal

Generate diagonal matrices.

Transposition

Transpose a matrix.

Uses Accelerate’s vDSP_mtrans/vDSP_mtransD.

Inversion

Calculate the inverse of a matrix.

Uses LAPACK’s sgetri_/dgetri_ for real matrices and cgetri_/zgetri_ for complex matrices.

Multiplication

<*> infix operator.

Implements matrix multiplication.

Uses Accelerate’s vDSP_mmul/vDSP_mmulD for real matrices and vDSP_zmmul/vDSP_zmmulD for complex matrices.

Division

/> and </ infix operators.

Implements left and right matrix division (multiplying by the inverse of a matrix).

Square Root

Complex square roots.

Formula taken from MATLAB’s sqrt function.

Exponentiation

Complex exponentials.

Formula taken from MATLAB’s exp function.

Products

Inner and outer products.

Eigendecomposition

Calculate the eigendecomposition of a matrix. Includes support for only calculating the necessary components. Also includes support for sorting the eigenvectors by properties of the eigenvalues.

Uses LAPACK’s sgeev_/dgeev_. Swift implementation cribbed from Surge.

Roots

Calculate the roots of a polynomial by taking the eigenvalues of a companion matrix.

Image Processing

Bitmaps

Conversion to and from floating point formats in the range 0.0...1.0 to 8-bit bitmaps in the range 0...255.

Images

Conversion to and from 8-bit bitmaps and CGImage, CIImage, NSImage, and UIImage.

Signal Processing

FFT

Forward and inverse two-dimensional fourier transforms.

Includes support for creating, reusing, and destroying your own FFTSetup/FFTSetupD structure.

Some of the inverse fourier transform methods implement energy conservation by dividing by the size of the matrix.

Uses Accelerate’s vDSP_fft2d_zip/vDSP_fft2d_zipD.

FFTShift

Apply a circular rotation to a frequency-domain matrix so that the DC/DC signal is at the top left of the lower right quadrant.

Autocorrelation

Calculate the autocorrelation of a matrix by taking the square magnitudes in the frequency domain.