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Basic foilset DoD HPF Training -- 2. Fortran90

Given by Chuck Koelbel -- Rice University at DoD Training and Others on 1995-98. Foils prepared August 7 98
Outside Index Summary of Material

Second Presentation in Chuck Koelbel's Tutorial Sequence on HPF
Short Overview of Fortran 90 for HPF users
  • What is Fortran90,95,2000
  • Memory Allocation, Array Operations, Intrinsics, Procedure Interfaces

Table of Contents for full HTML of DoD HPF Training -- 2. Fortran90

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1 "High Performance Fortran in Practice" tutorial 2. Fortran 90/95 Features
Presented at SIAM Parallel Processing San Francisco, Feb. 14, 1995
Presented at Supercomputer '95, Mannheim, Germany June 27, 1995
Presented at Supercomputing '95, San Diego, December 4, 1995
Presented at University of Tennessee (short form), Knoxville, March 21, 1996
Presented at Metacenter Regional Alliances, Cornell, May 6, 1996
Presented at Summer of HPF Workshop, Vienna, July 1, 1996
Presented at Institute for Mathematics & its Applications, Minneapolis, September 11-13, 1996
Presented at Corps of Engineers Waterways Experiments Station, Vicksburg, MS, October 30-November 1, 1996
Presented at Supercomputing '96, Pittsburgh, PA, November 17, 1996
Presented at NAVO, Stennis Space Center, MS, Feb 13, 1997
Presented at HPF Users Group (short version), Santa Fe, NM, February 23, 1997
Presented at ASC, Wright-Patterson Air Force Base, OH, March 5, 1997
Parts presented at SC'97, November 17, 1997
Parts presented (slideshow mode) at S '97, November 15-21, 1997
Presented at DOD HPC Users Group, June 1, 1998
2 Outline
3 Fortran 90
4 Fortran 95
5 Fortran 2000
6 Fortran 90/95 Memory Allocation
7 Typical Uses of Memory Allocation
8 Fortran 90/95 Array Operations
9 Typical Uses of Array Operations
10 Fortran 90/95 Intrinsics
11 Typical Uses of Intrinsics
12 Fortran 90/95 Procedure Interfaces
13 Typical Uses of Procedure Interfaces
14 Hints for Using Fortran 90/95

Outside Index Summary of Material

HTML version of Basic Foils prepared August 7 98

Foil 1 "High Performance Fortran in Practice" tutorial 2. Fortran 90/95 Features
Presented at SIAM Parallel Processing San Francisco, Feb. 14, 1995
Presented at Supercomputer '95, Mannheim, Germany June 27, 1995
Presented at Supercomputing '95, San Diego, December 4, 1995
Presented at University of Tennessee (short form), Knoxville, March 21, 1996
Presented at Metacenter Regional Alliances, Cornell, May 6, 1996
Presented at Summer of HPF Workshop, Vienna, July 1, 1996
Presented at Institute for Mathematics & its Applications, Minneapolis, September 11-13, 1996
Presented at Corps of Engineers Waterways Experiments Station, Vicksburg, MS, October 30-November 1, 1996
Presented at Supercomputing '96, Pittsburgh, PA, November 17, 1996
Presented at NAVO, Stennis Space Center, MS, Feb 13, 1997
Presented at HPF Users Group (short version), Santa Fe, NM, February 23, 1997
Presented at ASC, Wright-Patterson Air Force Base, OH, March 5, 1997
Parts presented at SC'97, November 17, 1997
Parts presented (slideshow mode) at S '97, November 15-21, 1997
Presented at DOD HPC Users Group, June 1, 1998

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
HTML version of Basic Foils prepared August 7 98

Foil 2 Outline

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
1. Introduction to Data-Parallelism
2. Fortran 90/95 Features *** This Presentation
3. HPF Parallel Features
4. HPF Data Mapping Features
5. Parallel Programming in HPF
6. HPF Version 2.0
HTML version of Basic Foils prepared August 7 98

Foil 3 Fortran 90

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Fortran 90 is a major extension of FORTRAN 77 including:
  • All of FORTRAN 77
  • Syntax Improvements
  • Memory Allocation
  • Array Features
  • New Intrinsics
  • Procedure Interfaces
  • Pointers
  • User-defined Types
Adopted by ANSI and ISO in 1991 (hence ³F90²)
HTML version of Basic Foils prepared August 7 98

Foil 4 Fortran 95

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Fortran 95 is the newest international standard for Fortran
  • Adopted by ISO in 1997 (hence ³F95²)
It is a small delta from Fortran 90
  • A very few features deleted from the language
    • Hollerith constants, real-valued DO indices, etc.
    • This won¹t happen again
  • FORALL, PURE, and ELEMENTAL added
    • FORALL and PURE from HPF
    • ELEMENTAL due to user requests
  • General clean-up of language features
HTML version of Basic Foils prepared August 7 98

Foil 5 Fortran 2000

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Work is progressing on Fortran 2000
  • It is expected to be adopted by ISO in 2002
F2K will be another major upgrade (although not so great as F90)
  • Object-oriented features
    • But not pervasive in the language!
    • Inheritance, runtime polymorphism if you ask for it
  • IEEE Floating Point exceptions
    • With partial implementations for hardware that doesn't support them
  • C interoperability
    • In a standard way
  • Interval arithmetic
HTML version of Basic Foils prepared August 7 98

Foil 6 Fortran 90/95 Memory Allocation

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
ALLOCATABLE arrays use heap storage
  • Declared without defined bounds
  • ALLOCATE & DEALLOCATE statements create and free storage
Local arrays use stack storage
  • Bounds may be non-constant, evaluated at procedure entry
  • E.g., local arrays the same size as a dummy parameter
Assumed-shape arrays can pass array sizes
  • Dummy parameters without declared bounds
  • Compiler passes bounds in a data descriptor
  • Bounds can be queried with intrinsics
HTML version of Basic Foils prepared August 7 98

Foil 7 Typical Uses of Memory Allocation

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Allocating arrays in main program
  • REAL, ALLOCATABLE :: u(:,:), f(:,:), r(:,:)
  • ALLOCATE( u(0:ni,0:nj), f(0:ni,0:nj), &
    • r(0:ni,0:nj) )
Passing assumed-shape arrays
  • INTERFACE
    • SUBROUTINE residual(x,y,z)
    • REAL x(:,:), y(:,:), z(:,:)
    • END SUBROUTINE
  • END INTERFACE
  • CALL residual( r, u, f )
  • CALL residual( r(0:ni:2,0:nj:2), &
    • u(0:ni:2,0:nj:2), f(0:ni:2,0:nj:2) )
HTML version of Basic Foils prepared August 7 98

Foil 8 Fortran 90/95 Array Operations

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Whole arrays and array subsections can be used in many operations formerly limited to scalar values.
  • Array arithmetic and assignment
  • WHERE (conditional assignment)
  • Vector subscripts
  • Subroutine arguments and return values
Subsections specified by triplet notation
  • A( lb : ub : step )
  • Defaults for missing lb, ub, or step
Array constructors to produce array-valued constants (with implied DO)
HTML version of Basic Foils prepared August 7 98

Foil 9 Typical Uses of Array Operations

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Scaling
  • REAL u(0:nx,0:ny), fact, avg
  • u = fact * (u - avg)
Computing a residual (version 1)
  • REAL r(0:nx,0:ny), u(0:nx,0:ny),f(0:nx,0:ny)
  • r(0:nx:jmp,0:ny:jmp)=-u(0:nx:jmp,0:ny:jmp)+ &
    • 0.25*(CSHIFT(u(0:nx:jmp,0:ny:jmp),1,1) + &
    • CSHIFT(u(0:nx:jmp,0:ny:jmp),-1,1) + &
    • CSHIFT(u(0:nx:jmp,0:ny:jmp),1,2) + &
    • CSHIFT(u(0:nx:jmp,0:ny:jmp),-1,2)) + &
    • f(0:nx:jmp,0:ny:jmp)
Computing a residual (version 2)
  • REAL r(:,:), u(:,:), f(:,:)
  • r = - u+0.25*(CSHIFT(u,1,1)+CSHIFT(u,-1,1)+ &
    • CSHIFT(u,1,2)+CSHIFT(u,-1,2)) + f
HTML version of Basic Foils prepared August 7 98

Foil 10 Fortran 90/95 Intrinsics

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Elemental intrinsics
  • Most familiar intrinsics can be applied to arrays
  • E.g., SQRT(A(1:100)) computes 100 square roots
Transformational intrinsics
  • Reductions combine elements in an array (or along one dimension at a time)
  • E.g., SUM(A) adds up the elements in A
  • Data movement operations perform structured transformations
  • E.g. TRANSPOSE(A) transposes A (2-D only)
Array query intrinsics
  • Useful for assumed-shape arrays
  • E.g., SIZE(A,1) gives the extent of A in the first dimension
HTML version of Basic Foils prepared August 7 98

Foil 11 Typical Uses of Intrinsics

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Initialization
  • REAL, ALLOCATABLE :: u(:,:)
  • CALL RANDOM_SEED
  • CALL RANDOM_NUMBER(u)
Computing the error
  • REAL r(0:nx,0:ny)
  • error_value = SQRT( SUM(r*r) )
Prolongation
  • REAL u(0:nx,0:ny)
  • u(0:nx:jmp2,jmp:ny:jmp2) = &
    • u(0:nx:jmp2,jmp:ny:jmp2)+&
    • 0.5*CSHIFT(u(0:nx:jmp2,jmp2:ny:jmp2),1,2)
HTML version of Basic Foils prepared August 7 98

Foil 12 Fortran 90/95 Procedure Interfaces

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Explicit and implicit interfaces
  • Explicit: in the same compilation unit, or imported interface
    • Required for certain uses such as POINTER dummies and assumed-shape array dummies
  • Implicit: as in FORTRAN 77
INTERFACE blocks provide explicit interfaces
  • Define types of parameters and return values
MODULE provides type-safe libraries
  • Contains declarations, functions, and type definitions
  • All interfaces collected in one place
  • PRIVATE data and procedures allowed
  • USE imports the interfaces
HTML version of Basic Foils prepared August 7 98

Foil 13 Typical Uses of Procedure Interfaces

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Option 1: Use Fortran 77-style arguments
  • CALL residual(r, u, f, ni, nj)
  • ! No way to pass every other element of r
Option 2: Use assumed-shape arrays
  • INTERFACE
    • SUBROUTINE residual(x,y,z)
    • REAL x(:,:), y(:,:), z(:,:)
    • END SUBROUTINE
  • END INTERFACE
  • CALL residual( r, u, f )
  • CALL residual( r(0:ni:2,0:nj:2), &
    • & u(0:ni:2,0:nj:2), f(0:ni:2,0:nj:2) )
HTML version of Basic Foils prepared August 7 98

Foil 14 Hints for Using Fortran 90/95

From DoD HPF Training -- 2. Fortran90 DoD Training and Others -- 1995-98. *
Full HTML Index
Declare arrays to be the natural size and shape
  • ALLOCATE in main routine (or when size is set)
  • Automatic local arrays
  • Assumed shape dummies (controversial)
Array operations are great for data parallelism
  • But they don't cover everythingŠ
Use MODULE and INTERFACE
  • Consistency checking for you
  • Extra information for the compiler
Complicated data structures are possible
  • Unclear what compilers will optimize well
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