filter.cs

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/*
 * Filter functions, a part of DSProcessing library.
 * author: Jan Sova
 * mailto: [e-mail]
 *
 * -------------------------------------------------------------------------
 *
 * DSProcessing - C#/C++ library of signal processing, speech processing,
 *              and communications classes and functions
 *
 * Copyright (C) 2007-2008
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * -------------------------------------------------------------------------
 */

using System;
using System.Collections.Generic;
using System.Text;

namespace DSProcessing
{
    class Filter
    {
        /// <summary>
        /// Fuction known from Matlab.
        /// </summary>
        /// <param name="b"></param>
        /// <param name="a"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static double[] filtfilt(double[] b, double[] a, double[] data)
        {
            //pripravna cast
            int nfilt = (int)Tools.max(b.Length, a.Length);
            int nfact = nfilt * 3 - 1;
            int len = data.Length;

            if (len <= nfact) // input data too short!
            {
                Console.WriteLine("input data too short!");
            }
            double[] d = new double[data.Length + 2 * nfilt];

            //interpolation
            for (int i = 0; i < nfilt; i++)
                d[i] = 2 * data[0] - data[nfilt + 1 - i];

            for (int i = nfilt; i < nfilt + data.Length; i++)
                d[i] = data[i - nfilt];

            int k = 0;
            for (int i = nfilt + data.Length; i < nfilt + data.Length; i++)
            {
                d[i] = 2 * data[data.Length] - data[nfilt - 2 - k];
                k++;
            }

            //2*x(1)-x((nfact+1):-1:2);x;2*x(len)-x((len-1):-1:len-nfact)];


            //filtration
            double[] x = filt(b, a, data);
            x = Tools.timereverse(x);
            double[] z = filt(b, a, x);
            z = Tools.timereverse(z);

            return z;
        }

        /// <summary>
        /// CZ: Jestli se nepletu, tak pole a[] a b[] museji byt stejne dlouha! Je to opravnene?
        /// EN: Filtration with filter given by a[]/b[].
        /// </summary>
        /// <param name="b"></param>
        /// <param name="a"></param>
        /// <param name="data"></param>
        /// <returns>a[] and b[] must be the same length</returns>
        public static double[] filt(double[] b, double[] a, double[] data)
        {
            double[] y = new double[data.Length];


            for (int i = 0; i < data.Length; i++)
                y[i] = 0;

            for (int n = 0; n < b.Length; n++)
            {
                int max = n;

                //CZ: zpetnovazebni cast
                for (int k = 0; k <= max; k++)
                    y[n] += b[k] * data[n - k];

                for (int k = 1; k <= max; k++)
                    y[n] -= a[k] * y[n - k];
            }

            for (int n = b.Length; n < data.Length; n++)
            {

                //dopredna cast
                for (int k = 1; k < a.Length; k++)
                    y[n] -= a[k] * y[n - k];

                //zpetnovazebni cast
                for (int k = 0; k < b.Length; k++)
                    y[n] += b[k] * data[n - k];
            }

            return y;
        }

        /// <summary>
        /// CZ: klouzavy prumer
        /// </summary>
        /// <param name="data"></param>
        /// <param name="M"></param>
        /// <returns></returns>
        public static double[] MAfilter(double[] data, int M)
        {
            double[] returnValue = new double[data.Length];

            //
            for (int n = M; n < data.Length; n++)
            {
                for (int m = 0; m <= M; m++)
                {
                    returnValue[n] += data[n - M];
                }

                returnValue[n] /= (M + 1);
            }

            //CZ: jeste doresit prvni vzorky
            for (int n = 0; n < M; n++)
            {
                int max = n;
                for (int m = 0; m <= max; m++)
                {
                    returnValue[n] += data[n - m];
                }

                returnValue[n] /= (max + 1);
            }

            return returnValue;
        }

        ///test sequence for N = 3
        ///in: 10, 12, 11, 0, 9, 8, 10, 15, 14, 100, 13, 20, 15
        ///out: 10, 11, 11, 9, 8, 9, 10, 14, 15, 14, 20, 15, 15
        ///test sequence for N = 5
        ///in: 10, 12, 11, 0, 9, 8, 10, 15, 14, 100, 13, 20, 15
        ///out: 10, 10, 10, 9, 9, 9, 10, 14, 14, 15, 15, 15, 13 
        /// <summary>
        /// Median filtration.
        /// </summary>
        /// <param name="data"></param>
        /// <param name="N">rank</param>
        /// <returns></returns>
        public static double[] medfilt1(double[] data, int N)
        {

            double[] returnValue = new double[data.Length];
            double[] data1 = new double[data.Length + (N / 2) * 2];
            double[] okno = new double[N];
            int NPul = N / 2;

            for (int i = 0; i < N / 2; i++)
                data1[i] = 0;

            for (int i = 0; i < data.Length; i++)
                data1[NPul + i] = data[i];
            for (int i = data.Length + NPul; i < data.Length + 2 * NPul; i++)
                data1[i] = 0;

            //CZ: pro sudy rad
            if ((N / 2) * 2 == N)
            {
                for (int i = 0; i < data1.Length - N; i++)
                {
                    for (int j = 0; j < N; j++)
                    {
                        okno[j] = data1[i + j];
                    }

                    returnValue[i] = Tools.mean(okno);
                }
            }
            //CZ: pro lichy rad
            else
            {
                for (int i = 0; i < data1.Length - N + 1; i++)
                {
                    for (int j = 0; j < N; j++)
                    {
                        okno[j] = data1[i + j];
                    }

                    //<todo>CZ: Implementovat lepsi tridici algoritmus</todo>

                    Tools.insertSort(okno);
                    returnValue[i] = okno[N / 2];
                }
            }

            return returnValue;
        }
    }
}