random number in interval of [-1,+1] 1

[Am_Ine]

Hi everyone,
I'm a new user of FORTRAN and i would like to write a subroutine in fortran to generate a random number between [-1 , +1]
actually i have written a simple one but , the number generated is between [0, +1] and in each time of compilation i have the same random number generated

i need help to fix this problem
i'm waiting for your answers ,
thanks in advance

 

[mikrom]

Hi Am_Ine,

You can generate random number 0 <= r <= 1 using the subroutine random_number(r)
Here is an example:

https://www.tek-tips.com/viewthread.cfm?qid=1594158

Then if you have r from [0, 1] then you can create a random number q from [A, B] as
q = A + (B - A) * r
so in your case for q from [-1 1] it will be
q = -1 + 2 * r

 

[Am_Ine]

thank you mikrom for your rapid and helpful answer
sorry but , please i have just one more question,
to generate differente random numbers each compilation , the function'' init_random-seed()'' doesn't works with me
i get :

/tmp/cc4kPuvl.o: In function `MAIN__':
main.f95.text+0x18): undefined reference to `init_random_seed_'
collect2: error: ld returned 1 exit status

do you have anby solution for that

 

[mikrom]

use the standard subroutine random_seed
or you can declare and use your own init_random_seed as shown here:

https://www.tek-tips.com/viewthread.cfm?qid=1789488

https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gfortran/RANDOM_005fSEED.html#RANDOM_005fSEED

 

[Am_Ine]

thank you mikrom for your help