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

NAG Workshop and Surgery 6 December 2001. Using the NAG Library from LabVIEW John Keightley NPL, Centre for Ionising Radiation Metrology. Outline of Talk. Basics of calling the NAG DLLs from LabVIEW Similarities with C/C++ calling conventions Introduction to LabVIEW “Call Library Function”

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

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  1. NAG Workshop and Surgery 6 December 2001 Using the NAG Library fromLabVIEWJohn KeightleyNPL, Centre for Ionising Radiation Metrology

  2. 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

  3. Parameter Types in Fortran and LabVIEW

  4. BASICS • Very similar approach to C/C++ • 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 );

  5. “Advanced” Functions Palette from VI diagram LAbVIEW “Call Library Function”

  6. Complex NumbersExample 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 );

  7. A02ABF : LabVIEW Call

  8. 2D Arrays • In FORTRAN : • 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)

  9. 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

  10. 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 ? ! ??????

  11. Correct Calling Convention: returning a character string

  12. A Simple Example : E02ADF and E02AEFCurve Fitting and Interpolation by Chebyshev Polynomials • Program Reads Input Data : • Least Squares Fitting by method of Chebyshev Polynomials • E02ADF • Interpolation of values • E02AEF

  13. Curve Fitting by Chebshev Polynomials

  14. Curve Fitting by Chebshev Polynomials

  15. Curve Fitting by Chebshev PolynomialsInterpolation

  16. 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 • );

  17. 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; }

  18. 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 ???

  19. 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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