/*************************************************************************
Copyright (c) 1992-2007 The University of Tennessee.  All rights reserved.

Contributors:
    * Sergey Bochkanov (ALGLIB project). Translation from FORTRAN to
      pseudocode.

See subroutines comments for additional copyrights.

>>> SOURCE LICENSE >>>
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 (www.fsf.org); 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.

A copy of the GNU General Public License is available at
http://www.fsf.org/licensing/licenses

>>> END OF LICENSE >>>
*************************************************************************/


namespace alglib {
  public class ssolve {
    /*************************************************************************
    Solving  a system  of linear equations  with a system matrix  given by its
    LDLT decomposition

    The algorithm solves systems with a square matrix only.

    Input parameters:
        A       -   LDLT decomposition of the matrix (the result of the
                    SMatrixLDLT subroutine).
        Pivots  -   row permutation table (the result of the SMatrixLDLT subroutine).
        B       -   right side of a system.
                    Array whose index ranges within [0..N-1].
        N       -   size of matrix A.
        IsUpper -   points to the triangle of matrix A in which the LDLT
                    decomposition is stored.
                    If IsUpper=True, the decomposition has the form of U*D*U',
                    matrix U is stored in the upper triangle of  matrix A  (in
                    that case, the lower triangle isn't used and isn't changed
                    by the subroutine).
                    Similarly, if IsUpper=False, the decomposition has the form
                    of L*D*L' and the lower triangle stores matrix L.

    Output parameters:
        X       -   solution of a system.
                    Array whose index ranges within [0..N-1].

    Result:
        True, if the matrix is not singular. X contains the solution.
        False, if the matrix is singular (the determinant of matrix D is equal
    to 0). In this case, X doesn't contain a solution.
    *************************************************************************/
    public static bool smatrixldltsolve(ref double[,] a,
        ref int[] pivots,
        double[] b,
        int n,
        bool isupper,
        ref double[] x) {
      bool result = new bool();
      int i = 0;
      int k = 0;
      int kp = 0;
      double ak = 0;
      double akm1 = 0;
      double akm1k = 0;
      double bk = 0;
      double bkm1 = 0;
      double denom = 0;
      double v = 0;
      int i_ = 0;

      b = (double[])b.Clone();


      //
      // Quick return if possible
      //
      result = true;
      if (n == 0) {
        return result;
      }

      //
      // Check that the diagonal matrix D is nonsingular
      //
      if (isupper) {

        //
        // Upper triangular storage: examine D from bottom to top
        //
        for (i = n - 1; i >= 0; i--) {
          if (pivots[i] >= 0 & (double)(a[i, i]) == (double)(0)) {
            result = false;
            return result;
          }
        }
      } else {

        //
        // Lower triangular storage: examine D from top to bottom.
        //
        for (i = 0; i <= n - 1; i++) {
          if (pivots[i] >= 0 & (double)(a[i, i]) == (double)(0)) {
            result = false;
            return result;
          }
        }
      }

      //
      // Solve Ax = b
      //
      if (isupper) {

        //
        // Solve A*X = B, where A = U*D*U'.
        //
        // First solve U*D*X = B, overwriting B with X.
        //
        // K+1 is the main loop index, decreasing from N to 1 in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = n - 1;
        while (k >= 0) {
          if (pivots[k] >= 0) {

            //
            // 1 x 1 diagonal block
            //
            // Interchange rows K+1 and IPIV(K+1).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(U(K+1)), where U(K+1) is the transformation
            // stored in column K+1 of A.
            //
            v = b[k];
            for (i_ = 0; i_ <= k - 1; i_++) {
              b[i_] = b[i_] - v * a[i_, k];
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            b[k] = b[k] / a[k, k];
            k = k - 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Interchange rows K+1-1 and -IPIV(K+1).
            //
            kp = pivots[k] + n;
            if (kp != k - 1) {
              v = b[k - 1];
              b[k - 1] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(U(K+1)), where U(K+1) is the transformation
            // stored in columns K+1-1 and K+1 of A.
            //
            v = b[k];
            for (i_ = 0; i_ <= k - 2; i_++) {
              b[i_] = b[i_] - v * a[i_, k];
            }
            v = b[k - 1];
            for (i_ = 0; i_ <= k - 2; i_++) {
              b[i_] = b[i_] - v * a[i_, k - 1];
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            akm1k = a[k - 1, k];
            akm1 = a[k - 1, k - 1] / akm1k;
            ak = a[k, k] / akm1k;
            denom = akm1 * ak - 1;
            bkm1 = b[k - 1] / akm1k;
            bk = b[k] / akm1k;
            b[k - 1] = (ak * bkm1 - bk) / denom;
            b[k] = (akm1 * bk - bkm1) / denom;
            k = k - 2;
          }
        }

        //
        // Next solve U'*X = B, overwriting B with X.
        //
        // K+1 is the main loop index, increasing from 1 to N in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = 0;
        while (k <= n - 1) {
          if (pivots[k] >= 0) {

            //
            // 1 x 1 diagonal block
            //
            // Multiply by inv(U'(K+1)), where U(K+1) is the transformation
            // stored in column K+1 of A.
            //
            v = 0.0;
            for (i_ = 0; i_ <= k - 1; i_++) {
              v += b[i_] * a[i_, k];
            }
            b[k] = b[k] - v;

            //
            // Interchange rows K+1 and IPIV(K+1).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k + 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Multiply by inv(U'(K+1+1)), where U(K+1+1) is the transformation
            // stored in columns K+1 and K+1+1 of A.
            //
            v = 0.0;
            for (i_ = 0; i_ <= k - 1; i_++) {
              v += b[i_] * a[i_, k];
            }
            b[k] = b[k] - v;
            v = 0.0;
            for (i_ = 0; i_ <= k - 1; i_++) {
              v += b[i_] * a[i_, k + 1];
            }
            b[k + 1] = b[k + 1] - v;

            //
            // Interchange rows K+1 and -IPIV(K+1).
            //
            kp = pivots[k] + n;
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k + 2;
          }
        }
      } else {

        //
        // Solve A*X = B, where A = L*D*L'.
        //
        // First solve L*D*X = B, overwriting B with X.
        //
        // K+1 is the main loop index, increasing from 1 to N in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = 0;
        while (k <= n - 1) {
          if (pivots[k] >= 0) {

            //
            // 1 x 1 diagonal block
            //
            // Interchange rows K+1 and IPIV(K+1).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(L(K+1)), where L(K+1) is the transformation
            // stored in column K+1 of A.
            //
            if (k + 1 < n) {
              v = b[k];
              for (i_ = k + 1; i_ <= n - 1; i_++) {
                b[i_] = b[i_] - v * a[i_, k];
              }
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            b[k] = b[k] / a[k, k];
            k = k + 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Interchange rows K+1+1 and -IPIV(K+1).
            //
            kp = pivots[k] + n;
            if (kp != k + 1) {
              v = b[k + 1];
              b[k + 1] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(L(K+1)), where L(K+1) is the transformation
            // stored in columns K+1 and K+1+1 of A.
            //
            if (k + 1 < n - 1) {
              v = b[k];
              for (i_ = k + 2; i_ <= n - 1; i_++) {
                b[i_] = b[i_] - v * a[i_, k];
              }
              v = b[k + 1];
              for (i_ = k + 2; i_ <= n - 1; i_++) {
                b[i_] = b[i_] - v * a[i_, k + 1];
              }
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            akm1k = a[k + 1, k];
            akm1 = a[k, k] / akm1k;
            ak = a[k + 1, k + 1] / akm1k;
            denom = akm1 * ak - 1;
            bkm1 = b[k] / akm1k;
            bk = b[k + 1] / akm1k;
            b[k] = (ak * bkm1 - bk) / denom;
            b[k + 1] = (akm1 * bk - bkm1) / denom;
            k = k + 2;
          }
        }

        //
        // Next solve L'*X = B, overwriting B with X.
        //
        // K+1 is the main loop index, decreasing from N to 1 in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = n - 1;
        while (k >= 0) {
          if (pivots[k] >= 0) {

            //
            // 1 x 1 diagonal block
            //
            // Multiply by inv(L'(K+1)), where L(K+1) is the transformation
            // stored in column K+1 of A.
            //
            if (k + 1 < n) {
              v = 0.0;
              for (i_ = k + 1; i_ <= n - 1; i_++) {
                v += b[i_] * a[i_, k];
              }
              b[k] = b[k] - v;
            }

            //
            // Interchange rows K+1 and IPIV(K+1).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k - 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Multiply by inv(L'(K+1-1)), where L(K+1-1) is the transformation
            // stored in columns K+1-1 and K+1 of A.
            //
            if (k + 1 < n) {
              v = 0.0;
              for (i_ = k + 1; i_ <= n - 1; i_++) {
                v += b[i_] * a[i_, k];
              }
              b[k] = b[k] - v;
              v = 0.0;
              for (i_ = k + 1; i_ <= n - 1; i_++) {
                v += b[i_] * a[i_, k - 1];
              }
              b[k - 1] = b[k - 1] - v;
            }

            //
            // Interchange rows K+1 and -IPIV(K+1).
            //
            kp = pivots[k] + n;
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k - 2;
          }
        }
      }
      x = new double[n - 1 + 1];
      for (i_ = 0; i_ <= n - 1; i_++) {
        x[i_] = b[i_];
      }
      return result;
    }


    /*************************************************************************
    Solving a system of linear equations with a symmetric system matrix

    Input parameters:
        A       -   system matrix (upper or lower triangle).
                    Array whose indexes range within [0..N-1, 0..N-1].
        B       -   right side of a system.
                    Array whose index ranges within [0..N-1].
        N       -   size of matrix A.
        IsUpper -   If IsUpper = True, A contains the upper triangle,
                    otherwise A contains the lower triangle.

    Output parameters:
        X       -   solution of a system.
                    Array whose index ranges within [0..N-1].

    Result:
        True, if the matrix is not singular. X contains the solution.
        False, if the matrix is singular (the determinant of the matrix is equal
    to 0). In this case, X doesn't contain a solution.

      -- ALGLIB --
         Copyright 2005 by Bochkanov Sergey
    *************************************************************************/
    public static bool smatrixsolve(double[,] a,
        ref double[] b,
        int n,
        bool isupper,
        ref double[] x) {
      bool result = new bool();
      int[] pivots = new int[0];

      a = (double[,])a.Clone();

      ldlt.smatrixldlt(ref a, n, isupper, ref pivots);
      result = smatrixldltsolve(ref a, ref pivots, b, n, isupper, ref x);
      return result;
    }


    public static bool solvesystemldlt(ref double[,] a,
        ref int[] pivots,
        double[] b,
        int n,
        bool isupper,
        ref double[] x) {
      bool result = new bool();
      int i = 0;
      int k = 0;
      int kp = 0;
      int km1 = 0;
      int km2 = 0;
      int kp1 = 0;
      int kp2 = 0;
      double ak = 0;
      double akm1 = 0;
      double akm1k = 0;
      double bk = 0;
      double bkm1 = 0;
      double denom = 0;
      double v = 0;
      int i_ = 0;

      b = (double[])b.Clone();


      //
      // Quick return if possible
      //
      result = true;
      if (n == 0) {
        return result;
      }

      //
      // Check that the diagonal matrix D is nonsingular
      //
      if (isupper) {

        //
        // Upper triangular storage: examine D from bottom to top
        //
        for (i = n; i >= 1; i--) {
          if (pivots[i] > 0 & (double)(a[i, i]) == (double)(0)) {
            result = false;
            return result;
          }
        }
      } else {

        //
        // Lower triangular storage: examine D from top to bottom.
        //
        for (i = 1; i <= n; i++) {
          if (pivots[i] > 0 & (double)(a[i, i]) == (double)(0)) {
            result = false;
            return result;
          }
        }
      }

      //
      // Solve Ax = b
      //
      if (isupper) {

        //
        // Solve A*X = B, where A = U*D*U'.
        //
        // First solve U*D*X = B, overwriting B with X.
        //
        // K is the main loop index, decreasing from N to 1 in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = n;
        while (k >= 1) {
          if (pivots[k] > 0) {

            //
            // 1 x 1 diagonal block
            //
            // Interchange rows K and IPIV(K).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(U(K)), where U(K) is the transformation
            // stored in column K of A.
            //
            km1 = k - 1;
            v = b[k];
            for (i_ = 1; i_ <= km1; i_++) {
              b[i_] = b[i_] - v * a[i_, k];
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            b[k] = b[k] / a[k, k];
            k = k - 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Interchange rows K-1 and -IPIV(K).
            //
            kp = -pivots[k];
            if (kp != k - 1) {
              v = b[k - 1];
              b[k - 1] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(U(K)), where U(K) is the transformation
            // stored in columns K-1 and K of A.
            //
            km2 = k - 2;
            km1 = k - 1;
            v = b[k];
            for (i_ = 1; i_ <= km2; i_++) {
              b[i_] = b[i_] - v * a[i_, k];
            }
            v = b[k - 1];
            for (i_ = 1; i_ <= km2; i_++) {
              b[i_] = b[i_] - v * a[i_, km1];
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            akm1k = a[k - 1, k];
            akm1 = a[k - 1, k - 1] / akm1k;
            ak = a[k, k] / akm1k;
            denom = akm1 * ak - 1;
            bkm1 = b[k - 1] / akm1k;
            bk = b[k] / akm1k;
            b[k - 1] = (ak * bkm1 - bk) / denom;
            b[k] = (akm1 * bk - bkm1) / denom;
            k = k - 2;
          }
        }

        //
        // Next solve U'*X = B, overwriting B with X.
        //
        // K is the main loop index, increasing from 1 to N in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = 1;
        while (k <= n) {
          if (pivots[k] > 0) {

            //
            // 1 x 1 diagonal block
            //
            // Multiply by inv(U'(K)), where U(K) is the transformation
            // stored in column K of A.
            //
            km1 = k - 1;
            v = 0.0;
            for (i_ = 1; i_ <= km1; i_++) {
              v += b[i_] * a[i_, k];
            }
            b[k] = b[k] - v;

            //
            // Interchange rows K and IPIV(K).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k + 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Multiply by inv(U'(K+1)), where U(K+1) is the transformation
            // stored in columns K and K+1 of A.
            //
            km1 = k - 1;
            kp1 = k + 1;
            v = 0.0;
            for (i_ = 1; i_ <= km1; i_++) {
              v += b[i_] * a[i_, k];
            }
            b[k] = b[k] - v;
            v = 0.0;
            for (i_ = 1; i_ <= km1; i_++) {
              v += b[i_] * a[i_, kp1];
            }
            b[k + 1] = b[k + 1] - v;

            //
            // Interchange rows K and -IPIV(K).
            //
            kp = -pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k + 2;
          }
        }
      } else {

        //
        // Solve A*X = B, where A = L*D*L'.
        //
        // First solve L*D*X = B, overwriting B with X.
        //
        // K is the main loop index, increasing from 1 to N in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = 1;
        while (k <= n) {
          if (pivots[k] > 0) {

            //
            // 1 x 1 diagonal block
            //
            // Interchange rows K and IPIV(K).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(L(K)), where L(K) is the transformation
            // stored in column K of A.
            //
            if (k < n) {
              kp1 = k + 1;
              v = b[k];
              for (i_ = kp1; i_ <= n; i_++) {
                b[i_] = b[i_] - v * a[i_, k];
              }
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            b[k] = b[k] / a[k, k];
            k = k + 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Interchange rows K+1 and -IPIV(K).
            //
            kp = -pivots[k];
            if (kp != k + 1) {
              v = b[k + 1];
              b[k + 1] = b[kp];
              b[kp] = v;
            }

            //
            // Multiply by inv(L(K)), where L(K) is the transformation
            // stored in columns K and K+1 of A.
            //
            if (k < n - 1) {
              kp1 = k + 1;
              kp2 = k + 2;
              v = b[k];
              for (i_ = kp2; i_ <= n; i_++) {
                b[i_] = b[i_] - v * a[i_, k];
              }
              v = b[k + 1];
              for (i_ = kp2; i_ <= n; i_++) {
                b[i_] = b[i_] - v * a[i_, kp1];
              }
            }

            //
            // Multiply by the inverse of the diagonal block.
            //
            akm1k = a[k + 1, k];
            akm1 = a[k, k] / akm1k;
            ak = a[k + 1, k + 1] / akm1k;
            denom = akm1 * ak - 1;
            bkm1 = b[k] / akm1k;
            bk = b[k + 1] / akm1k;
            b[k] = (ak * bkm1 - bk) / denom;
            b[k + 1] = (akm1 * bk - bkm1) / denom;
            k = k + 2;
          }
        }

        //
        // Next solve L'*X = B, overwriting B with X.
        //
        // K is the main loop index, decreasing from N to 1 in steps of
        // 1 or 2, depending on the size of the diagonal blocks.
        //
        k = n;
        while (k >= 1) {
          if (pivots[k] > 0) {

            //
            // 1 x 1 diagonal block
            //
            // Multiply by inv(L'(K)), where L(K) is the transformation
            // stored in column K of A.
            //
            if (k < n) {
              kp1 = k + 1;
              v = 0.0;
              for (i_ = kp1; i_ <= n; i_++) {
                v += b[i_] * a[i_, k];
              }
              b[k] = b[k] - v;
            }

            //
            // Interchange rows K and IPIV(K).
            //
            kp = pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k - 1;
          } else {

            //
            // 2 x 2 diagonal block
            //
            // Multiply by inv(L'(K-1)), where L(K-1) is the transformation
            // stored in columns K-1 and K of A.
            //
            if (k < n) {
              kp1 = k + 1;
              km1 = k - 1;
              v = 0.0;
              for (i_ = kp1; i_ <= n; i_++) {
                v += b[i_] * a[i_, k];
              }
              b[k] = b[k] - v;
              v = 0.0;
              for (i_ = kp1; i_ <= n; i_++) {
                v += b[i_] * a[i_, km1];
              }
              b[k - 1] = b[k - 1] - v;
            }

            //
            // Interchange rows K and -IPIV(K).
            //
            kp = -pivots[k];
            if (kp != k) {
              v = b[k];
              b[k] = b[kp];
              b[kp] = v;
            }
            k = k - 2;
          }
        }
      }
      x = new double[n + 1];
      for (i_ = 1; i_ <= n; i_++) {
        x[i_] = b[i_];
      }
      return result;
    }


    public static bool solvesymmetricsystem(double[,] a,
        double[] b,
        int n,
        bool isupper,
        ref double[] x) {
      bool result = new bool();
      int[] pivots = new int[0];

      a = (double[,])a.Clone();
      b = (double[])b.Clone();

      ldlt.ldltdecomposition(ref a, n, isupper, ref pivots);
      result = solvesystemldlt(ref a, ref pivots, b, n, isupper, ref x);
      return result;
    }
  }
}