Beefy Boxes and Bandwidth Generously Provided by pair Networks
Keep It Simple, Stupid
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
I'm not a c compiler expert, but have a look at double precision pi It may be the difference between computational precision and "%Lf" display precision. I started looking into it, when I questioned the way GLib defined pi as a constant. They defined it out to 50 decimal places, but any use of it in it's long double is limited to 15 decimal places.

One of the c gurus in that thread said that c's precision is only gauranteed to 10 decimal places, but with IEEE standards, it's common to see 15. I see 15.

Eventually, I found mpfr which lets you set how many digits of precision you want to use.

If you can show me a simple c program that computes and displays values out to 50 decimal places, with normal c, I would be greatful. Everything I see truncates it (pi) to 3.(15 decimal places).

For example, in this code, the value of pi is correctly printed as a string on the first line of output, but the subsequent lines all have garbage after the 15th decimal place.

#include <gtk/gtk.h> /* gcc -o test test.c `pkg-config --cflags --libs gtk+-2.0` */ int main (){ /* how the headers define G_PI */ /* #define G_PI 3.1415926535897932384626433832795028841971693993751 + */ long double PI = G_PI; g_print("3.1415926535897932384626433832795028841971693993751\n"); g_print("%0.50e\n",G_PI); g_print("%0.50Lf\n",G_PI); g_print("%0.50Lf\n",PI); g_print("%0.50Lg\n",PI); g_print("%0.50Le\n",PI); return 0; }
Output:
^^^^^^^^^^^ -> unstable after 15 dec +imal 3.1415926535897932384626433832795028841971693993751 3.14159265358979311599796346854418516159057617187500e+00 -0.00000000000000000000000000000000000000000000000000 3.14159265358979311599796346854418516159057617187500 3.141592653589793115997963468544185161590576171875 3.14159265358979311599796346854418516159057617187500e+00 ^^^^^^^^^^^^ -> unstable after 15 dec +imal

I'm not really a human, but I play one on earth. Cogito ergo sum a bum

In reply to Re^3: RFC: Getting Started with PDL (the Perl Data Language) by zentara
in thread RFC: Getting Started with PDL (the Perl Data Language) by lin0

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others cooling their heels in the Monastery: (3)
As of 2022-08-16 02:00 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found

    Notices?