text: //------------------------------------------------------------------------------
  // GB_mex_concat: C = concat (Tiles)
  //------------------------------------------------------------------------------
  
  // SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2021, All Rights Reserved.
  // SPDX-License-Identifier: Apache-2.0
  
  //------------------------------------------------------------------------------
  
  #include "GB_mex.h"
  
  #define USAGE "C = GB_mex_concat (Tiles, type, fmt)"
  
  #define FREE_ALL                                \
  {                                               \
      if (Tiles != NULL)                          \
      {                                           \
          for (int64_t k = 0 ; k < m*n ; k++)     \
          {                                       \
              GrB_Matrix_free_(&(Tiles [k])) ;    \
          }                                       \
      }                                           \
      mxFree (Tiles) ;                            \
      GrB_Matrix_free_(&C) ;                      \
      GB_mx_put_global (true) ;                   \
  }
  
  #define OK(method)                      \
  {                                       \
      info = method ;                     \
      if (info != GrB_SUCCESS)            \
      {                                   \
          printf ("%d at %d\n", info, __LINE__) ;  \
          mexErrMsgTxt ("failed") ;       \
      }                                   \
  }
  
  void mexFunction
  (
      int nargout,
      mxArray *pargout [ ],
      int nargin,
      const mxArray *pargin [ ]
  )
  {
  
      GrB_Info info ;
      bool malloc_debug = GB_mx_get_global (true) ;
      GrB_Matrix C = NULL ;
      GrB_Matrix *Tiles = NULL ;
      int64_t m = 0, n = 0 ;
  
      // check inputs
      if (nargout > 1 || nargin < 1 || nargin > 3)
      {
          mexErrMsgTxt ("Usage: " USAGE) ;
      }
  
      // get Tiles (shallow copy)
      const mxArray *mxTiles = pargin [0] ;
      if (!mxIsCell (mxTiles))
      {
          FREE_ALL ;
          mexErrMsgTxt ("Tiles must be a cell array") ;
      }
      m = mxGetM (mxTiles) ;
      n = mxGetN (mxTiles) ;
      Tiles = mxMalloc (m * n * sizeof (GrB_Matrix)) ;
      for (int64_t j = 0 ; j < n ; j++)
      {
          for (int64_t i = 0 ; i < m ; i++)
          {
              // get the Tiles {i,j} matrix.
              // Tiles is row-major but mxTiles is column-major
              mxArray *Tile = mxGetCell (mxTiles, i+j*m) ;
              Tiles [i*n+j] = GB_mx_mxArray_to_Matrix (Tile, "Tile", false, true);
          }
      }
  
      // get the type of C, default is double
      GrB_Type ctype = GB_mx_string_to_Type (PARGIN (1), GrB_FP64) ;
  
      // determine the # of rows of C from Tiles {:,0}
      GrB_Index cnrows = 0 ;
      for (int64_t i = 0 ; i < m ; i++)
      {
          GrB_Index anrows ;
          OK (GrB_Matrix_nrows (&anrows, Tiles [i*n])) ;
          cnrows += anrows ;
      }
  
      // determine the # of columms of C from Tiles {0,:}
      GrB_Index cncols = 0 ;
      for (int64_t j = 0 ; j < n ; j++)
      {
          GrB_Index ancols ;
          OK (GrB_Matrix_ncols (&ancols, Tiles [j])) ;
          cncols += ancols ;
      }
  
      // get the format of C, default is by column
      int GET_SCALAR (2, int, fmt, GxB_BY_COL) ;
  
      // construct the empty C
      #define GET_DEEP_COPY                               \
          GrB_Matrix_new (&C, ctype, cnrows, cncols) ;    \
          GxB_Matrix_Option_set_(C, GxB_FORMAT, fmt) ;
      #define FREE_DEEP_COPY  GrB_Matrix_free_(&C) ;
      GET_DEEP_COPY ;
  
      // C = concat (Tiles)
      METHOD (GxB_Matrix_concat (C, Tiles, m, n, NULL)) ;
  
      // return C to MATLAB as a struct and free the GraphBLAS C
      pargout [0] = GB_mx_Matrix_to_mxArray (&C, "C output", true) ;
      FREE_ALL ;
  }
  
  