KING

data type

• there are only these data type in the MPI

  • if you want to use struct or multi array, you need to do something else

• 	MPI data type	c data type
  	MPI_CHAR	signed char|
  	MPI_SHORT	signed short int|
  	MPI_INT	signed int|
  	MPI_LONG	signed long int|
  	MPI_UNSIGNED_CHAR	unsigned long int|
  	MPI_UNSIGNED_SHORT	unsigned short int|
  	MPI_UNSIGNED	unsigned int|
  	MPI_FLOAT	float|
  	MPI_DOUBLE	double|
  	MPI_LONG_DOUBLE	long double|
  	MPI_BYTE	|
  	MPI_MPI_PACKED	|

about the status

• the MPI_status combine a lots of information
  • there are at least three member in the status
    • MPI_SOURCE, MPI_TAG, MPI_ERROR
• and we can get the size of the message using
  • MPI_Get_Count(MPI_Status status, MPI_Datatype datatype, int count_ptr);

The broadcast idea

• you can use the MPI_Bcast idea to send the message to all the other process;
  • MPI_Bcast(void *message, int count, MPI_Datatype datatype, int root, MPI_Comm comm)

gather the data and scatter the data

• use MPI_Gather
  • MPI_Gather(void send_data, int send_count, MPI_Datatype send_type, void recv_data, int recv_count, MPI_Datatype recv_type, int root, MPI_Comm comm)
• use MPI_Scatter to scatter the data
  • MPI_Scatter(void send_data, int send_count, MPI_Datatype send_type, void recv_data, int recv_count, MPI_Datatype recv_type, int root, MPI_Comm comm);
  • MPI_Scatter split the data referenced by send_data on the process with rank root into k segment.each of which consists of send_count elements of type send_type.