mathnet-numerics/src/Numerics/Algorithms/LinearAlgebra/ManagedLinearAlgebra.cs

// <copyright file="ManagedLinearAlgebra.cs" company="Math.NET">
// Math.NET Numerics, part of the Math.NET Project
// http://mathnet.opensourcedotnet.info
// Copyright (c) 2009 Math.NET
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using System;
using MathNet.Numerics.Threading;

namespace MathNet.Numerics.Algorithms.LinearAlgebra
{
    /// <summary>
    /// The managed linear algebra provider.
    /// </summary>
    internal class ManagedLinearAlgebra : ILinearAlgebra
    {
        /// <summary>
        /// Adds a scaled vector to another: <c>y += alpha*x</c>.
        /// </summary>
        /// <param name="y">The vector to update.</param>
        /// <param name="alpha">The value to scale <param name="x"/> by.</param>
        /// <param name="x">The vector to add to <paramref name="y"/>.</param>
        /// <remarks>This equivalent to the AXPY BLAS routine.</remarks>
        public void AddVectorToScaledVector(double[] y, double alpha, double[] x)
        {
            if (y == null)
            {
                throw new ArgumentNullException("y");
            }

            if (x == null)
            {
                throw new ArgumentNullException("x");
            }

            if (y.Length != x.Length)
            {
                throw new ArgumentException(Properties.Resources.ArgumentVectorsSameLength);
            }

            if (alpha.AlmostZero())
            {
                return;
            }

            if (alpha.AlmostEqual(1.0))
            {
                Parallel.For(0, y.Length, i => y[i] += x[i]);
            }
            else
            {
                Parallel.For(0, y.Length, i => y[i] += alpha * x[i]);
            }
        }

        public void ScaleArray(double alpha, double[] x)
        {
            if (alpha.AlmostEqual(1.0))
            {
                return;
            }
            Parallel.For(0, x.Length, i => x[i] = alpha * x[i]);
        }
    }
}