Argument of ZGEQRF -> what is COMPLEX*16 ?

[Mat]

Hello,

i don't know how to use methods which handle with complex input. For example the complex QR factorization ZGEQRF.

In the function documentation the usage is described:
A (input/output) COMPLEX*16 array, dimension (LDA,N)

But what is an COMPLEX*16 array?

For complex values there is the real and complex part of a number. What input is expected. I think i cannot create any array with a self-defined structure as data element for the array. Or how has the array to be defined?

Thanks for any help

[Julie]

Mat,
DOUBLE COMPLEX or COMPLEX*16 is a Fortran "double complex" data type, two 64-bit floating point doubles;
COMPLEX is a Fortran "complex" data type, two 32-bit floating point reals

The difference between these two is the precision. They both are regular complex number with a real and a imaginary part.

To declare your double complex array, do a simple:

Code: Select all

COMPLEX*16 MYARRAY(LDA,N)

Hope it helps
Julie

[Mat]

Thanks Julie,

sorry for my lack of knowledge.
I'm using lapack with C/C++ so ....is it possible that i have to use a structure of real and image part of a number for input?

Further help would be very nice :wink:

[Julie]

Mat,

Complex is not defined in C.
But ISO C99 introduces support for complex numbers in C. This is done with a new type qualifier, complex. It is a keyword if and only if `complex.h' has been included. There are three complex types, corresponding to the three real types: float complex, double complex, and long double complex.

Julie

[Mat]

Thanks a lot....

i found this page:
http://docs.sun.com/app/docs/doc/802-29 ... 7t8?a=view

Isn't it possible to pass to do something like this:

struct complex{double r, double i;}

complex *arr = new complex[5];

//fill arr...

_zgeqrf(m, n, arr,....);

[Julie]

Yes sure, no problem
Julie