psb_halo — Halo Data Communication

5.1 psb_halo — Halo Data Communication

These subroutines gathers the values of the halo elements:

x ← x

where:

x: is a global dense submatrix.


α, x	Subroutine

Integer	psb_halo
Short Precision Real	psb_halo
Long Precision Real	psb_halo
Short Precision Complex	psb_halo
Long Precision Complex	psb_halo

Table 17: Data types

call psb_halo(x, desc_a, info)
call psb_halo(x, desc_a, info, work, data)

Type:: Synchronous.
On Entry
x: global dense matrix x.
Scope: local
Type: required
Intent: inout.
Specified as: a rank one or two array or an object of type psb_T_vect_type containing numbers of type specified in Table 17.
desc_a: contains data structures for communications.
Scope: local
Type: required
Intent: in.
Specified as: a structured data of type psb_desc_type.
work: the work array.
Scope: local
Type: optional
Intent: inout.
Specified as: a rank one array of the same type of x.
data: index list selector.
Scope: global
Type: optional
Specified as: an integer. Values:psb_comm_halo_,psb_comm_mov_, psb_comm_ext_, default: psb_comm_halo_. Chooses the index list on which to base the data exchange.
On Return
x: global dense result matrix x.
Scope: local
Type: required
Intent: inout.
Returned as: a rank one or two array containing numbers of type specified in Table 17.
info: the local portion of result submatrix y.
Scope: local
Type: required
Intent: out.
An integer value that contains an error code.

Figure 7: Sample discretization mesh.

Usage Example Consider the discretization mesh depicted in fig. 7, partitioned among two processes as shown by the dashed line; the data distribution is such that each process will own 32 entries in the index space, with a halo made of 8 entries placed at local indices 33 through 40. If process 0 assigns an initial value of 1 to its entries in the x vector, and process 1 assigns a value of 2, then after a call to psb_halo the contents of the local vectors will be the following:

Process 0			Process 1
I	GLOB(I)	X(I)	I	GLOB(I)	X(I)
1	1	1.0	1	33	2.0
2	2	1.0	2	34	2.0
3	3	1.0	3	35	2.0
4	4	1.0	4	36	2.0
5	5	1.0	5	37	2.0
6	6	1.0	6	38	2.0
7	7	1.0	7	39	2.0
8	8	1.0	8	40	2.0
9	9	1.0	9	41	2.0
10	10	1.0	10	42	2.0
11	11	1.0	11	43	2.0
12	12	1.0	12	44	2.0
13	13	1.0	13	45	2.0
14	14	1.0	14	46	2.0
15	15	1.0	15	47	2.0
16	16	1.0	16	48	2.0
17	17	1.0	17	49	2.0
18	18	1.0	18	50	2.0
19	19	1.0	19	51	2.0
20	20	1.0	20	52	2.0
21	21	1.0	21	53	2.0
22	22	1.0	22	54	2.0
23	23	1.0	23	55	2.0
24	24	1.0	24	56	2.0
25	25	1.0	25	57	2.0
26	26	1.0	26	58	2.0
27	27	1.0	27	59	2.0
28	28	1.0	28	60	2.0
29	29	1.0	29	61	2.0
30	30	1.0	30	62	2.0
31	31	1.0	31	63	2.0
32	32	1.0	32	64	2.0
33	33	2.0	33	25	1.0
34	34	2.0	34	26	1.0
35	35	2.0	35	27	1.0
36	36	2.0	36	28	1.0
37	37	2.0	37	29	1.0
38	38	2.0	38	30	1.0
39	39	2.0	39	31	1.0
40	40	2.0	40	32	1.0

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