gsl seeding random number generator

Hi, I'm trying to use gsl to provide random numbers for my program. I can get the basic defaults to work, but I was trying to get this part:
"By setting the two variables on the command line we can change the default generator and the seed,
$ GSL_RNG_TYPE="taus" GSL_RNG_SEED=123 ./a.out"

I'm using a compiler where you just have to hit a key to get it to compile/run, but there's a box where you can add command line options, so I did, but nothing changed. I have a feeling I'm just doing something stupid because I'm not used to talking about these things, but does anyone have any suggestions?

Are those command-line options for the compiler, or for when you actually run the program?

I guess I can't tell for sure. I've gotten pretty confused because I've been trying to figure everything out at once. I think I was assuming for running the program...
This is where I was looking for one of the programs I was trying to duplicate:
http://www.gnu.org/software/gsl/manu...variables.html

Hi,

They are environmental variables for your shell, have a look at the example source code.

Cheers,

Dan.

Quote:

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Originally Posted by sqytoad

I guess I can't tell for sure. I've gotten pretty confused because I've been trying to figure everything out at once. I think I was assuming for running the program...
This is where I was looking for one of the programs I was trying to duplicate:
http://www.gnu.org/software/gsl/manu...variables.html

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Yes. we know they're command-line options for running the program -- I mean the box you're trying to type them into! Is that for running the compiler, or the program? (If the former, then you're in the wrong box.)

Yeah, that's where I've been looking, but I wasn't sure exactly how to change them...

Here is a list of some other RNG

e.g if you want gfsr4 RNG then,

GSL_RNG_TYPE="gfsr4"

then if you want use a different seed,

GSL_RNG_SEED=983759

then just run your code as normal from the command line.

Full description of the RNG (e.g. use the string after the last underscore as the abbreviation in you GSL_RNG_TYPE variable).

Oh, sorry, tabstop, my bad. lol I'm not 100% sure it's not a box for the compiler, but I'm definitely not using the one in compiler options. I'll look and see again if there's another box somewhere, but in any case, do you think I just need the "GSL_RNG_SEED=123" part, or would I need the full line starting with the $? I don't know if it's implied since it's in the box.

EDIT: Oh, and boyfarrell, I've been looking at those pages, but my question is really just about the command line stuff in general, since I haven't had to do anything with it before - I just hit a key. So I've been trying to figure that stuff out. It doesn't seem complicated, but I haven't gotten it to work, yet... :(

Quote:

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Originally Posted by sqytoad

Oh, sorry, tabstop, my bad. lol I'm not 100% sure it's not a box for the compiler, but I'm definitely not using the one in compiler options. I'll look and see again if there's another box somewhere, but in any case, do you think I just need the "GSL_RNG_SEED=123" part, or would I need the full line starting with the $? I don't know if it's implied since it's in the box.

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The $ is the command prompt. You know, the thing the computer puts on the screen to tell you that it's your turn to do something. The two variable names and the values are what you're looking for. What IDE are you using?

(Note: It may be easier to do this in a command prompt window.)

Oh, that actually explains some of my confusion from reading about this stuff... :S
I'm using dev-C++.

In Dev-C++, the only box that might have worked was Execute->Parameters, but that goes after the program name, not before.

You can change environment variables from the Control Panel, or at a command prompt window.

All right, thanks.
Do I need to figure out how to run/compile completely from the command-prompt window, or is there a way to change them and still run it like I'm used to?

(And how do you do it form the control panel?)

Control Panel -> System -> Advanced tab -> Environment variables button (If you do this, you can just hit the button, you don't need to type.)

Once you've compiled it with Ctrl-F9, you have to remember where the executable went, go to that directory, and type the magic words.

Thank you SO much.

Hey, so actually it seems you can use this function, as well, to change the seed:
void gsl_rng_set (const gsl_rng * r, unsigned long int s).
From this page
http://www.gnu.org/software/gsl/manu...alization.html
I was trying some things, but now I'm at loss as to how to actually do it. How do I actually set the seed as something else? :S

The first argument is a pointer to your random number generator state, and the second argument is the seed.

Right, but I guess I don't know how to make the result actually depend on s...

Quote:

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Originally Posted by sqytoad

Right, but I guess I don't know how to make the result actually depend on s...

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That's not your job, that's the job of the people who made the random number generator. All your job is, is to feed s into the function.

In other words: I have no idea what you think you're asking here.

I'm sorry, I have been really confusing.
I've been messing with one of their sample programs, and it basically goes through like this.
T = gsl_rng_taus2;
r = gsl_rng_alloc (T);
printf ("%e\n", gsl_rng_uniform (r));

But changing s isn't as simple as just having
s=123;
gsl_rng_set (r,s)

because that doesn't do anything. The sample from the generator just depends on r, the seed should affect r since it affects the generator T...
And I don't really know...sorry I'm being so vague, but I just don't know how to get it to work.

I don't have GSL installed, unfortunately, so I can't try it out, but doesn't this:

Code:

---

T = gsl_rng_taus2;
r = gsl_rng_alloc(T);
gsl_rng_set(r, 123L);
for (int i=0; i < 5; i++) {
    printf("&#37;e\n", gsl_rng_uniform(r));
}
printf("\n");
gsl_rng_set(r, 123L);
for (int i=0; i < 5; i++) {
    printf("%e\n", gsl_rng_uniform(r));
}

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print out the same five numbers, twice in a row? (If you'll pardon the C99 for loops.)

Yeah, it did. (Assuming you meant the same sequence of 5 different numbers, twice.)

Why do you have the L after 123?
Because that makes sense to me...I wasn't really doing much different.

"L" means long.

Oh, all right.
Well, everything works now. Seriously, thanks a lot for your patience.