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**NAG Workshop and Surgery**

6 December 2001 Using the NAG Library from LabVIEW John Keightley NPL, Centre for Ionising Radiation Metrology

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**Outline of Talk Basics of calling the NAG DLLs from LabVIEW**

Similarities with C/C++ calling conventions Introduction to LabVIEW “Call Library Function” Problems I’ve encountered so far !! Complex Numbers 2D Arrays must be TRANSPOSED ! Functions and Subroutines Character Strings returned via function name Arrays MUST be large enough to hold output Example

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**Parameter Types in Fortran and LabVIEW**

INTEGER I32 or “signed long int” REAL Double (8 bytes) LOGICAL COMPLEX double re, double im CHARACTER*n Blank character string, I32 for string length EXTERNAL ? ? ? ? ? Don’t know how !!

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**BASICS Very similar approach to C/C++ Ie: C++ header from NAG help**

C/C++ headers are VERY useful in determining calling notation for LabVIEW NB : Stdcall(WINAPI) calling convention Ie: C++ header from NAG help extern void __stdcall E02ACF( CONST double x[], CONST double y[], CONST int *n, double aa[], CONST int *m1, double *ref );

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**LAbVIEW “Call Library Function”**

“Advanced” Functions Palette from VI diagram

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**Complex Numbers Example A02ABF :Complex Modulus**

FORTRAN : real FUNCTION A02ABF(XR,XI) real XR,XI Refer to C/C++ headers (type definitions) typedef struct { double re,im; } Complex; ??? “Call Library Function” does not allow pointer to a “cluster” !! Refer to C/C++ header for A02ABF extern double __stdcall A02ABF( CONST double *xxr, CONST double *xxi );

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A02ABF : LabVIEW Call

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**2D Arrays In FORTRAN : In LabVIEW Thus, MUST TRANSPOSE arrays**

Column major order In LabVIEW Row major order (Same as C/C++) Thus, MUST TRANSPOSE arrays BEFORE inputting to NAG functions in the DLLs AFTER retrieving output from the DLLs. Can use LabVIEW “Transpose 2D Array” function from the Array palette ! or use the NAG routine F01CRF (more complicated as you need to know the size of the array to start with)

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**FORTRAN Subroutines and Functions**

SUBROUTINE returns VOID FUNCTION returns a value !! eg: SUBROUTINE X05AAF(ITIME) INTEGER ITIME(7) time data array passed through parameter list CHARACTER*30 FUNCTION X05ABF(ITIME) INTEGER ITIME(7) function returns a character array

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**Returning a character string via a function name**

CHARACTER*30 FUNCTION X05ABF(ITIME) INTEGER ITIME(7) Fortran has no NULL TERMINATED strings: Instead it uses TWO parameters for strings character string AND an int for string length cannot return TWO values !! Refer to C headers for solution : extern void __stdcall X05ABF (char [], int, CONST int itime[] ); 1st 2 parameters refer to string which was being returned via function name ? ! ??????

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**Correct Calling Convention: returning a character string**

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**A Simple Example : E02ADF and E02AEF Curve Fitting and Interpolation by Chebyshev Polynomials**

Program Reads Input Data : Least Squares Fitting by method of Chebyshev Polynomials E02ADF Interpolation of values E02AEF

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**Curve Fitting by Chebshev Polynomials**

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**Curve Fitting by Chebshev Polynomials**

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**Curve Fitting by Chebshev Polynomials Interpolation**

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**MY BIG PROBLEM : EXTERNAL calls**

Example : C05AJF : locates zero of a user supplied continuous function C/C++ header extern void __stdcall C05AJF( double *x, CONST double *eps, CONST double *eta, double (__stdcall *f)(double *), CONST int *nfmax, int *ifail );

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**EXTERNAL calls : C05AJF #include <math.h>**

#include <stdio.h> #include "nagmk19.h“ main(){ double eps, eta, x; int ifail, k, nfmax; double __stdcall f(double *); for (k=1; k<=2; k++){ eps = k==1 ? 0.1e-3 : 0.1e-4; x = 1.0; eta = 0.0; nfmax = 200; ifail = 1; C05AJF(&x,&eps,&eta,f,&nfmax,&ifail); if (ifail==0) printf("With eps = %e root = %f\n",eps,x); else{ printf("ifail = %d\n",ifail); if (ifail==3 | ifail==4) printf("With eps = %e final value = %f\n",eps,x); } return 0; double __stdcall f(double *x) { return exp(-*x) - *x; EXTERNAL calls : C05AJF

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**EXTENAL CALLS I DON’T KNOW HOW TO DO THIS IN LabVIEW !!**

ie: I need a pointer to the user supplied function !!! LabVIEW call library function doesn’t help me ! Wrapper DLL in C++ required ???

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**Conclusion Use LabVIEW “Call Library Function”**

LabVIEW calls are VERY SIMILAR to those in C/C++ Use NAG C headers for help ! Still to resolve issues with EXTERNAL calls to user supplied functions !! Nick Williamson from National Instruments is looking into this Wrapper DLL in C/C++ ?? I can help anyone wanting to use the NAG DLLs from LabVIEW !

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