NAG Technical Report 3/2009

Calling NAG Library Routines from Octave

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3.2. Example 2


Scaled complex complement of error function, exp(-z2)erfc(-iz) - nag_complex_erfc (s15ddc) routine

Here we show how to call a function with complex input and output values.


  1. Function prototype from the NAG C Library Manual
  2. C++ function
  3. Compiling into Oct-File
  4. Calling the function
  1. Function prototype from the NAG C Library Manual

    According to the C Library Manual, the prototype for function s15ddc looks like this:

      #include <nag.h>
      #include <nags.h>
      Complex nag_complex_erfc(Complex z, NagError *fail);
    The function takes two arguments. The first one is of type Complex and is the argument z of the function. The second argument to s15ddc is the error handling argument fail which is of type NagError. See the NAG C Library Manual for more information about the NagError type. To keep things simple we are not going to try to pass the contents of the NagError structure back to Octave. Instead, we will return only integer value of fail.code.
  2. C++ function

    Here is the source code of our C++ function

    #undef Complex
    #define Complex OctComplex
    #include <octave/oct.h>
    #undef Complex
    #define Complex NagComplex
    #define MatrixType NagMatrixType
    #include <nag.h>
    #include <nags.h>
    DEFUN_DLD (nag_cmplx_erfc, args, ,
      "Calls nag_complex_erfc (s15ddc), which computes values \n\
    of the function w(z)=e^(-z^2)erfc-iz, for complex z.\n")
     // Variable to store function output values
     octave_value_list retval;
     // Retrieve input arguments from args
     OctComplex z = args(0).complex_value();
     // Local variables
     NagError fail;
     OctComplex w;
     NagComplex z_nag, w_nag;
     // Copy the input OctComplex variable into NagComplex one = z.real(); = z.imag();
      // Call NAG routine like in C
      w_nag = nag_complex_erfc(z_nag,&fail);
      // Copy the output NagComplex variable into OctComplex one
      w.real() =;
      w.imag() =;
      // Assign output arguments to retval
      retval(0) = w;
      retval(1) = fail.code;
      return retval;

    Points to note about this code:

  3. Compiling into Oct-File

    To compile the C++ function into oct-files, we use the mkoctfile script supplied with Octave:

      % mkoctfile -L/opt/NAG/cll6a08dg/lib -lnagc_nag -I/opt/NAG/cll6a08dg/include
  4. Calling the function

    Assuming that all has gone well, we can call the function as if it was part of Octave itself, i.e. either from the Octave command line or from within an Octave program. An example call may be:
    octave:1> z=complex(-3.01,0.75)
    z = -3.01000 + 0.75000i
    octave:2> [w,ifail]=nag_cmplx_erfc(z)
    w =  0.052156 - 0.183776i
    ifail = 0

    (If you get an error message saying that a library cannot be located, see the tip given in Example 1).

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