psb_gedot -- Dot Product

This function computes dot product between two vectors $x$ and $y$.
If $x$ and $y$ are real vectors it computes dot-product as:

$$dot \leftarrow x^T y$$

Else if $x$ and $y$ are complex vectors then it computes dot-product as:

$$dot \leftarrow x^H y$$

psb_gedot(x, y, desc_a, info [,global])

Table 2: Data types

$dot$, $x$, $y$	Function
Short Precision Real	psb_gedot
Long Precision Real	psb_gedot
Short Precision Complex	psb_gedot
Long Precision Complex	psb_gedot

Type:

Synchronous.

On Entry

x

the local portion of global dense matrix $x$.
Scope: local
Type: required
Intent: in.
Specified as: a rank one or two array or an object of type vdatapsb_T_vect_type containing numbers of type specified in Table 2. The rank of $x$ must be the same of $y$.

y

the local portion of global dense matrix $y$.
Scope: local
Type: required
Intent: in.
Specified as: a rank one or two array or an object of type vdatapsb_T_vect_type containing numbers of type specified in Table 2. The rank of $y$ must be the same of $x$.

desc_a

contains data structures for communications.
Scope: local
Type: required
Intent: in.
Specified as: an object of type descdatapsb_desc_type.

global

Specifies whether the computation should include the global reduction across all processes.
Scope: global
Type: optional.
Intent: in.
Specified as: a logical scalar. Default: global=.true.

On Return

Function value

is the dot product of vectors $x$ and $y$.
Scope: global unless the optional variable global=.false. has been specified
Specified as: a number of the data type indicated in Table 2.

info

Error code.
Scope: local
Type: required
Intent: out.
An integer value; 0 means no error has been detected.

Notes

1. The computation of a global result requires a global communication, which entails a significant overhead. It may be necessary and/or advisable to compute multiple dot products at the same time; in this case, it is possible to improve the runtime efficiency by using the following scheme:
   
   In this way the global communication, which for small sizes is a latency-bound operation, is invoked only once.