9.4.2 Performing Multiplications

The user interacts with the library through CLA_Matrix_interface objects. Their constructor takes no arguments. A call to make_multiplier (described below) will properly initialize them. The class has two methods the user needs to use. First, is the multiply method. It has the following signature:

void multiply(double alpha, double beta, double *data, void (*fptr) (void *),
              void *usr_data, int x, int y);

Each element of the user's and arrays must call this method to perform the multiplication.

• The parameters alpha and beta correspond to and in . The same value must be passed for each of these two parameters at each elemnts of and .

• The paremeter data specifies where the data to be mutiplier is held. This is a two-dimensional array stored in a one-dimensional array. The size of the array is determined at creation time (based on user paremeters) and does not have to be specified at this point. For and data should contain the matrices to be multiplied. For , it is the destination where the result will be stored (and if , the data which will be multiplied by and added to ).

• The fptr paremeter specifies the callback which the library calls (at array when the computation is complete. When it is called, it passes usr_data to it. Only the elements of the array must specify a non-null value for fptr.

• The values of x and y specify the coordinates of the calling element in the users chare array (these should always be thisIndex.x and thisIndex.y, respectively).

The second function of the CLA_Matrix_interface objects is the sync method. This should be called at each element of the array when it is ready to migrate. It takes as arguments two intergers, x and y, which should always be thisIndex.x and thisIndex.y, respectively. Note that migration is currently only supported for the ``2D'' algorithm.