Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!sun-barr!newstop!texsun!convex!bleikamp
From: bleikamp@convex.com (Richard Bleikamp)
Newsgroups: comp.lang.fortran
Subject: Re: vectorization question
Summary: Fortran 90 aids to vectorization
Keywords: Fortran 90
Message-ID: <1991Mar29.195509.2323@convex.com>
Date: 29 Mar 91 19:55:09 GMT
References: <1991Mar29.141313.7418@ariel.unm.edu> <1991Mar29.165126.11431@rice.edu>
Sender: usenet@convex.com (news access account)
Organization: Convex Computer Corporation, Richardson, Tx.
Lines: 38
Nntp-Posting-Host: mozart.convex.com

In article <1991Mar29.165126.11431@rice.edu> paco@rice.edu (Paul Havlak) writes:
>
>In article <1991Mar29.141313.7418@ariel.unm.edu>, prentice@triton.unm.edu (John Prentice) writes:
>|> Consider the following loop:
>|> 
>|>       do 30 k=1,kmax
>|> 	  do 20 j=1,jmax
>|> 	      do 10 i=1,imax
>|> 		  a(i,j,k)=...
>|>    10         continue
>|>    20     continue
>|>    30 continue
>|> 
>|> On the Cray, only the inner most loop will vectorize. 
>|> ...
>
> useful discussion deleted.
>
>Good news about Fortran 90:  You can write the above loop in triplet notation:
>
>	a(1:imax,1:jmax,1:kmax) = ...
>
> more discussion deleted.
>
>Paul Havlak

Note that substituting Fortran 90 array notation is ONLY valid when the
assignment statement "a(i,j,k)= ..." does NOT contain a loop carried dependency.

It can be non-trivial (in complicated loops) to decide if any dependencies
exist.  When they do, you can sometimes rewrite the loop nest as two or more
separate Fortran 90 assignment statements, but sometimes there is no
semantically equivalent array notation.  

--
------------------------------------------------------------------------------
Rich Bleikamp			    bleikamp@convex.com
Convex Computer Corporation