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Introduction to Fortran95 Programming Part II By Deniz Savas, CiCS, 2007 dsavas@clemson

Introduction to Fortran95 Programming Part II By Deniz Savas, CiCS, 2007 dsavas@clemson.edu. Part II: Contents. Data Declarations and Specifications ARRAYS and Array Handling Where & Forall statements. Data Specifications & Declarations. Type declarations ( built in and user-defined)

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Introduction to Fortran95 Programming Part II By Deniz Savas, CiCS, 2007 dsavas@clemson

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  1. Introduction to Fortran95 Programming Part II By Deniz Savas, CiCS, 2007 dsavas@clemson.edu

  2. Part II: Contents • Data Declarations and Specifications • ARRAYS and Array Handling • Where & Forall statements

  3. Data Specifications & Declarations • Type declarations ( built in and user-defined) • IMPLICIT statement • PARAMETER statement • DIMENSION statement • DATA statements • SAVE statement • USE statement

  4. Type Declarations Syntax: type [,attribute] :: list TYPE can be one of ; INTEGER ( KIND= n) - REAL ( KIND=n) COMPLEX( KIND= n ) - LOGICAL(KIND=n) CHARACTER ( LEN=m,KIND=n) • where (KIND=n) is OPTIONAL TYPE ( type-name) ATTRIBUTE can be a combination of; PARAMETER - PUBLIC - PRIVATE POINTER - TARGET - ALLOCATABLE DIMENSION - INTENT(inout) - OPTIONAL SAVE - EXTERNAL - INTRINSIC

  5. Example Type Declarations • Old Style (FTN77) INTEGER N , M PARAMETER ( N = 20 , M=30) REAL X , Y , Z, PI DIMENSION X(N) , Y(N) , Z(N) DATA PI / 3.1416 / • New Style (FTN90 onwards) INTEGER, PARAMETER :: N =20 , M = 30 REAL, DIMENSION(N) :: X , Y , Z REAL :: PI = 3.146 Note: The above two code segments are identical in effect.

  6. Example use of KIND valuesin variable declarations INTEGER , PARAMETER :: SMLINT=SELECTED_INT_KIND(2) INTEGER , PARAMETER :: BIGINT=SELECTED_INT_KIND(7) INTEGER,PARAMETER :: BIG=SELECTED_REAL_KIND(7,40) INTEGER(KIND=SMLINT) :: I , J , K INTEGER(KIND=BIGINT) :: ISUM , JSUM REAL ( KIND=BIG) :: A , B ,C The Intrinsic function KIND( )returns the kind value of its argument. EXAMPLE: IKIND = KIND(1.0E60)

  7. User Defined Types Also referred as Derived-Data-Types or Structures EXAMPLE: TYPE VERTEX REAL X , Y, Z END TYPE VERTEX TYPE ( VERTEX ) :: CORNER1 , CORNER2 CORNER2%Y = 2.5 ; CORNER1=( 1.0,1.0,0.2)

  8. Derived Types ( Examples) TYPE VERTEX REAL :: X , Y, Z END TYPE VERTEX TYPE PATCH TYPE ( VERTEX ) :: CORNER(4) END PATCH TYPE (VERTEX) :: P1 , P2, P3 , P4 TYPE (PATCH) :: MYPATCH , YOURPATCH P1 = ( 0.0 , 0.0 , 0.0 ) ; P3 = ( 1.0 , 1.0 , 0.0 ) P2 = ( 1.0 , 0.0 , 0.0 ) ; P4 = ( 0.0 , 1.0 , 0.0 ) MYPATCH = ( P1 , P2, P3,P4 ) YOURPATCH = MYPATCH YOURPATCH%CORNER(1) = MYPATCH%CORNER(4) - & (1.0,1.0,1.0)

  9. Derived Types ( More Examples) TYPE USERNAME CHARACTER*2 :: DEPARTMENT INTEGER :: STATUS CHARACTER*4 :: INITIALS TYPE ( USERNAME ) , POINTER :: NEIGHBOUR END TYPE USERNAME TYPE ( USERNAME ) , DIMENSION(1000) :: USERS USERS(1) = ( ‘CS’ , 1 , ‘DS’ ) USERS(12) = (‘CS’ , 1 , ‘PF’ ) USERS(1)%NEIGHBOUR => USERS(12) NULLIFY( USERS(12)%NEIGHBOUR )

  10. Array Declarations • STATIC INTEGER, PARAMETER :: N = 36 REAL :: A( 20) , B(-1:5) , C(4,N,N) , D(0:N,0:4) INTEGER , DIMENSION(10,10) :: MX ,NX,OX Note that up to 7 dimensional arrays are allowed. • ALLOCATABLE ( Dynamic global memory allocation) REAL, ALLOCATABLE :: A(:) , B(:,:,:) • AUTOMATIC( Dynamic local memory allocation) REAL, DIMENSION SIZE(A) :: work • ASSUMED SHAPE ( Used for declaring arrays passed to procedures ) REAL A(* )! Fortran77 syntax REAL :: A(:)! or A(:,:) so on Fortran90 syntax

  11. Allocatable Array Examples Used for declaring arrays whose size will be determined during run-time. REAL, ALLOCATABLE :: X(:) , Y(:,:) , Z(:) : READ(*,*) N ALLOCATE( X(N) ) ALLOCATE ( Y(-N:N,0:N ) , STATUS=status) ALLOCATE ( Z(SIZE(X) ) : DEALLOCATE ( X,Y,Z) END

  12. Assumed Shape Array Examples Used for declaring the dummy array arguments’ dimensions to procedures when these vary from call to call. PROGRAM TEST REAL :: AX1(20) , AX2(30) , AY(10,10) , BX1(80) , BX2(90),BY(20,30) : Call spline( AX1, AX2, AY) Call spline (BX1, BX2, BY) : END SUBROUTINE SPLINE( X1 , X2 , Y ) REAL , DIMENSION(:) :: X1 , X2 REAL , DIMENSION(:,:) :: Y : RETURN END

  13. Automatic Array Examples Use this method when you need short term storage for intermediate results. WORK arrays in NAG library are good examples ! SUBROUTINE INTERMIT( X1 , X2 , Y ,M) REAL , DIMENSION(:) :: X1 , X2 , Y INTEGER :: M REAL , DIMENSION(SIZE(Y) ) :: WORK COMPLEX , DIMENSION(M) :: CWORK : RETURN END

  14. Array Terminology • RANK , EXTENT, SHAPE and SIZE Determines the conformance • CONFORMANCE REAL A( 4,10) , B( 0:3,10) , C( 4,5,2) , D(0:2 , -1:4 , 6 ) A & B are: rank=2, extents=4 and 10 shape=4,10, size=40 C is rank=3, extents=4,5and 2 - shape=4,5,2 - size=40 D is rank=3 - extents=3 , 6 and 6 - shape=3,6,6 - size= 108 For two arrays to be conformable their rank, shape and size must match up. Above only A and B are conformable with each other.

  15. Whole Array Operations • Whole array operations can be performed on conformable arrays. This avoids using DO loops. REAL :: A(10,3,4) , B( 0:9,3,2:5) , C(0:9,0:2,0:4) : C = A + B ; C = A*B ; B= C/A ; C =sqrt(A) All the above array expressions are valid.

  16. WHERE Statement • This feature is a way of implementing vector operation masks. It can be seen as the vector equivalent of the IF statement WHERE (logical_array_expr ) array_var=array_expr WHERE (logical_array_expr ) array_assignments ELSE WHERE array_assignments END WHERE Note: ELSE WHERE clause is optional.

  17. Examples of where REAL :: A(300) , B(300) WHERE ( A > 1.0 ) A = 1.0/A WHERE ( A > B) A = B END WHERE WHERE ( A > 0.0 .AND. A>B ) A = LOG10( A ) ELSEWHERE A = 0.0 END WHERE

  18. FORALL statement This is a new Fortran95 feature. Extending the ability of Fortran Array Processing that was introduced by the WHERE statement. Syntax: FORALL (index=subscript_triplet, scalar_mask_expression) block of executable statements END FORALL

  19. FORALL statement example FORALL ( II=1:100,A(II)>0 ) X(II)=X(II)+Y(II) Y(II)= Y(II) * X(II) END FORALL Mask is elements of A between 1 and 100 whose values are positive

  20. Referencing Array Elements REAL A (10) , X(10,20,30) , value INTEGER I , K(10) value = A( 8)OK VALUE = A(12) WRONG !!!! I = 2; value = A( I )OK J = 3 ; I = 4 ; VALUE = X ( J, 10 , I )OK Value = X (1.5 ) WRONG !!! X(:,1,1) = A(K) !OK assuming K has values within the range 1 to 10

  21. Referencing Array Sections REAL :: A(10) , B(4,8) , C(4,5,6) I = 2 ; J=3 ; K=4 Referencing the array elements: A(2) B(3,4) C( 3,1,1) A(K) B(I,4) C(I,J,K) Referencing the array section: A(2:5) B(1,1:6) C( 1:1,3:4, 1:6 ) A(I:K) B( I:J,K) C(1:I,1:J,5 )

  22. Referencing Array Sections (cont.) It is also possible to use a stride index when referring to array sections. The rule is : array(start-index:stop-index:stride , ….) Stride can be a negative integer. If start-index is omitted it is assumed to be the lower_bound If stop-index is omitted it is assumed to be the upper_bound For example if array A is declared with DIMENSION(10,20) we can reference a subsections that contains only the even colums as; A(2:10:2,: ) The following are some other examples: A(1:9:3,1:20:2) this is the same as A(1:9:3,::2) A(10:1:-1,: ) this reverses the ordering of first dimension

  23. Array Intrinsics • Many of the elemental numeric functions such as those listed below can be called with array arguments to return array results ( of same shape and size). abs , sin, acos , exp , log , int , sqrt ... • There are also additional Vector/Matrix algebra functions designed to perform vector/matrix operations: dot_product , matmul , transpose , minval , sum , size , lbound , ubound , merge , maxloc , pack

  24. Array Assignments REAL A(10,10) , B(10) , C(0:9) , D(0:30) A = 1.0 ; B=0.55 B = (/ 3. , 5. ,6. ,1., 22. ,8. ,16. , 4. ,9. , 12.0 /) I = 3 C = A( I,1:10) D(11:20) = A(I+1,1:10) D(1:10) = D(11:20) D(3:10) = D(5:12) A(2,:) = SIN( B )

  25. Acknowledgement &References: • Thanks to Manchester and North High Performance Computing, Training & Education Centre for the Student Notes. • See APPENDIX A of the above notes for a list of useful reference books • Fortran 90 for Scientists and Engineers, Brian D Hahn, ISBN 0-340-60034-9 • Fortran 90 Explained by Metcalf & Reid is available from Blackwells ‘ St Georges Lib.’ Oxford Science Publications, ISBN 0-19-853772-7

  26. THE END

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