Converting arb_t to a double

[Valentina Sarti]

Dear All,

I am newbie to Flint, and I am currently using it since I need to use in my calculation a confluent hypergeometric function with complex arguments (acb_hypgeom_1f1).

I am currently at this stage of my dedicated function:

    acb_t result_acb;
    acb_init(result_acb);
    int regularized = 0;
    acb_hypgeom_1f1(result_acb, eta_acb, 0, zeta_acb, regularized, 64);

and now I would need simply to store the real and imaginary part of the result_acb into a std::complex<double> result (acb_realref(result_acb), acb_imagref(result_acb));

So I am facing the issue to convert the output of acb_realref to a double.
I need this since in my code then I use other libraries (gsl,etc...) and all the remaining calculations use double objects.

Can you provide me some suggestions in how to do this?

Thanks in advance!!

Valentina

[Fredrik Johansson]

Hello Valentina,

The easiest way to accomplish this is to use the ready-made wrapper in arb_fpwrap.h. See the example code here: https://github.com/flintlib/flint/blob/main/examples/fpwrap.c. In your case you would call arb_fpwrap_cdouble_hypgeom_1f1.

If you want to wrap the acb function yourself, the way to convert back to doubles is

double real = arf_get_d(arb_midref(acb_realref(z)), ARF_RND_NEAR);

double imag = arf_get_d(arb_midref(acb_imagref(z)), ARF_RND_NEAR);

Best,

Fredrik

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[Valentina Sarti]

Dear Fredrik,

thanks so much for the help!! 

Everything now runs, hopefully also the numbers will make sense :)!

Thanks again!!!

Best,

Valentina