1  /* ----------------------------------------------------------------------
  2   * Project:      CMSIS DSP Library
  3   * Title:        arm_mat_solve_lower_triangular_f64.c
  4   * Description:  Solve linear system LT X = A with LT lower triangular matrix
  5   *
  6   * $Date:        23 April 2021
  7   * $Revision:    V1.9.0
  8   *
  9   * Target Processor: Cortex-M and Cortex-A cores
 10   * -------------------------------------------------------------------- */
 11  /*
 12   * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
 13   *
 14   * SPDX-License-Identifier: Apache-2.0
 15   *
 16   * Licensed under the Apache License, Version 2.0 (the License); you may
 17   * not use this file except in compliance with the License.
 18   * You may obtain a copy of the License at
 19   *
 20   * www.apache.org/licenses/LICENSE-2.0
 21   *
 22   * Unless required by applicable law or agreed to in writing, software
 23   * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 24   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 25   * See the License for the specific language governing permissions and
 26   * limitations under the License.
 27   */
 28  
 29  #include "dsp/matrix_functions.h"
 30  
 31  /**
 32    @ingroup groupMatrix
 33   */
 34  
 35  
 36  /**
 37    @addtogroup MatrixInv
 38    @{
 39   */
 40  
 41  
 42     /**
 43     * @brief Solve LT . X = A where LT is a lower triangular matrix
 44     * @param[in]  lt  The lower triangular matrix
 45     * @param[in]  a  The matrix a
 46     * @param[out] dst The solution X of LT . X = A
 47     * @return The function returns ARM_MATH_SINGULAR, if the system can't be solved.
 48     */
 49    arm_status arm_mat_solve_lower_triangular_f64(
 50    const arm_matrix_instance_f64 * lt,
 51    const arm_matrix_instance_f64 * a,
 52    arm_matrix_instance_f64 * dst)
 53    {
 54    arm_status status;                             /* status of matrix inverse */
 55  
 56  
 57  #ifdef ARM_MATH_MATRIX_CHECK
 58  
 59    /* Check for matrix mismatch condition */
 60    if ((lt->numRows != lt->numCols) ||
 61        (lt->numRows != a->numRows)   )
 62    {
 63      /* Set status as ARM_MATH_SIZE_MISMATCH */
 64      status = ARM_MATH_SIZE_MISMATCH;
 65    }
 66    else
 67  
 68  #endif /* #ifdef ARM_MATH_MATRIX_CHECK */
 69  
 70    {
 71      /* a1 b1 c1   x1 = a1
 72            b2 c2   x2   a2
 73               c3   x3   a3
 74  
 75      x3 = a3 / c3 
 76      x2 = (a2 - c2 x3) / b2
 77  
 78      */
 79      int i,j,k,n,cols;
 80  
 81      float64_t *pX = dst->pData;
 82      float64_t *pLT = lt->pData;
 83      float64_t *pA = a->pData;
 84  
 85      float64_t *lt_row;
 86      float64_t *a_col;
 87  
 88      n = dst->numRows;
 89      cols = dst->numCols;
 90  
 91      for(j=0; j < cols; j ++)
 92      {
 93         a_col = &pA[j];
 94  
 95         for(i=0; i < n ; i++)
 96         {
 97              float64_t tmp=a_col[i * cols];
 98  
 99              lt_row = &pLT[n*i];
100  
101              for(k=0; k < i; k++)
102              {
103                  tmp -= lt_row[k] * pX[cols*k+j];
104              }
105  
106              if (lt_row[i]==0.0)
107              {
108                return(ARM_MATH_SINGULAR);
109              }
110              tmp = tmp / lt_row[i];
111              pX[i*cols+j] = tmp;
112         }
113  
114      }
115      status = ARM_MATH_SUCCESS;
116  
117    }
118  
119    /* Return to application */
120    return (status);
121  }
122  /**
123    @} end of MatrixInv group
124   */