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**Combining NCL and Fortran in C-shell**

#!/usr/bin/csh # =========== NCL ============ cat >! main.ncl << "END_NCL" load ”$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl" load ”$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl“ load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl“ external SUB "./sub.so" ; sub.so created below begin ... NCL script(s) end "END_NCL" # ===========FORTRAN ======== cat >! sub.f << "END_SUBF" C NCLFORTSTART ... can be many fortran codes …. C NCLEND "END_SUBF" # =========== WRAPIT========== WRAPIT sub.f # =========== EXECUTE ======== ncl main.ncl >&! main.out This can be convenient when debugging an NCL-Fortran script

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Accessing LAPACK (1 of 2) double precision LAPACK (BLAS) => distributed with NCL explicitly link LAPACK lib via fortran interface: WRAPIT eg LAPACK subroutine dgels solves [over/under] determined real linear system create an interface subroutine (here: dgels_interface.f) C NCLFORTSTART SUBROUTINE DGELSI( M, N, NRHS, A, B, LWORK, WORK ) IMPLICIT NONE INTEGER M, N, NRHS, LWORK DOUBLE PRECISION A( M, N ), B( M, NRHS), WORK(LWORK) C NCLEND C declare local variables INTEGER INFO CHARACTER*1 TRANS TRANS = "N” CALL DGELS(TRANS, M,N,NRHS,A,LDA,B,LDB,WORK,LWORK,INFO) RETURN END WRAPIT –L $NCARG_ROOT/lib -l lapack_ncl dgels_interface.f

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**Accessing LAPACK (2 of 2) external DGELS "./dgels_interface.so”**

; NAG example: ; These are transposed from the fortran example A = (/ (/ -0.57, -1.93, 2.30, -1.93, 0.15, /), \ ; (4,6) (/ -1.28, 1.08, 0.24, 0.64, 0.30, /), \ (/ -0.39, -0.31, 0.40, -0.66, 0.15, /), \ (/ 0.25, -2.14,-0.35, 0.08,-2.13, /) /)*1d0 ; must be double dimA = dimsizes(A) N = dimA(0) ; 4 M = dimA(1) ; 6 B = (/-2.67 ,-0.55 ,3.34, -0.77, 0.48, 4.10/)*1d ; must be double ; LAPACK wants 2D nrhs = 1 B2 = conform_dims ( (/nrhs,M/), B, 1 ) ; (1,6) B2(0,:) = B lwork = ; allocate space work = new ( lwork, "double", "No_FillValue") ; must be double DGELS::dgelsi(M, N, nrhs, A , B2, lwork, work ) ; call interface print(B2(0,0:N-1))

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**Global Variables and Scope [1 of 2]**

by definition: can be accessed from any function or procedure different from local variables NCL does not have explicit “global variables” requires understanding of NCL’s variable scope [identical to Pascal] load “dummy_1.ncl” ; not aware of constants below GRAVITY = 9.8 RGAS = 204 load “dummy_2.ncl” ; can use GRAVITY and RGAS REARTH = ; km load “dummy_3.ncl” ; can use GRAVITY, RGAS, REARTH begin ; can use GRAVITY, RGAS, REARTH : end

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**Global Variables and Scope [2 of 2]**

knowledgeable user can simulate … one approach create a file, eg GLOBAL.ncl (no: begin / end ) populate with desired constants best to follow some user defined conventions [e.g. capital letters to ensure uniqueness] ; contents of GLOBAL.ncl GRAVITY = ; = “m/s” GRAVITY_d = 9.81d ; m/s (type double) RDRY = ; J/(kg-K) REARTH = ; km load "/my/path/GLOBAL.ncl“ load "foo_1.ncl“ ; can ‘see’ constants in GLOBAL.ncl begin ; main script ; can ‘see’ constants in GLOBAL.ncl … end

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list variable [1 of 3] ‘container’ for one or more variables of any type (file, string, numeric) elements of a list are accessed via square brackets […] three ways to create a variable of type list f = addfiles(…) x = [/…/] ; list constructor a = NewList(…) q = addfiles (fil_names, "r") ; q is of type “list” x = q[:]->X ; [:] mean all elements of list s = q[2:8:2]->X ; extract x from files 2,4,6,8 f = addfile(…., “r”) ; type file i = ispan(1,10,2) ; integer z = (/ “example”, “wkshop”/) ; array constructor variable (/.../) delete( [/ f, i, z /] ) ; delete multiple variables

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list variable [2 of 3] r = random_normal(mean, stdev, N) ; create numeric variable s = (/ “sample” , “string” /) ; create a string variable lst = NewList (“fifo”) ; create a list variable ListPush (lst, r ) ; add ‘r’ to ‘lst’ ListPush (lst, r^2 ) ; add r^2 ListPush (lst, s ) ; add s nlst = ListCount( lst ) ; number of items in ‘lst’ do n=0,nlst-1 print( lst[n] ) ; print contents of list item ‘n’, use […] end do

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**list variable [3 of 3] function foo(….)**

A list variable may be used to return multiple variables from a function Similar to (say) Matlab ……. but not as nice function foo(….) begin x = … some calculation … ; x(:,:,:) with meta data s = (/ “string1”, “string2”/) ; s(2) … s(0)=“string1”, s(1)=”string2” z = … some calculation … ; z(:) return( [/s, x, z /]) ; return multiple variables as a list end ; Main ….. NCL code ….. result = foo(…) ; result is a list variable s = result[0] ; explicitly extract each variable x = result[1] ; convenience/clarity only z = result[2] delete(result) ; no longer needed Could access list elements directly but it is cumbersome, less clear print( result[0](1) ) ; “string2” …. not at all clear

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