// <copyright file="UnitPreconditioner.cs" company="Math.NET">
// Math.NET Numerics, part of the Math.NET Project
// http://numerics.mathdotnet.com
// http://github.com/mathnet/mathnet-numerics
//
// Copyright (c) 2009-2014 Math.NET
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
// </copyright>

using System;

namespace IStation.Numerics.LinearAlgebra.Solvers
{
    /// <summary>
    /// A unit preconditioner. This preconditioner does not actually do anything
    /// it is only used when running an <see cref="IIterativeSolver{T}"/> without
    /// a preconditioner.
    /// </summary>
    public sealed class UnitPreconditioner<T> : IPreconditioner<T> where T : struct, IEquatable<T>, IFormattable
    {
        /// <summary>
        /// The coefficient matrix on which this preconditioner operates.
        /// Is used to check dimensions on the different vectors that are processed.
        /// </summary>
        int _size;

        /// <summary>
        /// Initializes the preconditioner and loads the internal data structures.
        /// </summary>
        /// <param name="matrix">
        /// The matrix upon which the preconditioner is based.
        /// </param>
        /// <exception cref="ArgumentException">If <paramref name="matrix"/> is not a square matrix.</exception>
        public void Initialize(Matrix<T> matrix)
        {
            if (matrix.RowCount != matrix.ColumnCount)
            {
                throw new ArgumentException("Matrix must be square.", nameof(matrix));
            }

            _size = matrix.RowCount;
        }

        /// <summary>
        /// Approximates the solution to the matrix equation <b>Ax = b</b>.
        /// </summary>
        /// <param name="rhs">The right hand side vector.</param>
        /// <param name="lhs">The left hand side vector. Also known as the result vector.</param>
        /// <exception cref="ArgumentException">
        ///   <para>
        ///     If <paramref name="rhs"/> and <paramref name="lhs"/> do not have the same size.
        ///   </para>
        ///   <para>
        ///     - or -
        ///   </para>
        ///   <para>
        ///     If the size of <paramref name="rhs"/> is different the number of rows of the coefficient matrix.
        ///   </para>
        /// </exception>
        public void Approximate(Vector<T> rhs, Vector<T> lhs)
        {
            if ((lhs.Count != rhs.Count) || (lhs.Count != _size))
            {
                throw new ArgumentException("All vectors must have the same dimensionality.");
            }

            rhs.CopyTo(lhs);
        }
    }
}