What is wrong? A "random-" problem. Python. Please help!

[Skrutten]

I wonder how the random.normalvariate function works. When I do the method below, I end up with negative numbers. I don't want that. How do I prevent that?

And also, i want 10 numbers, but it always turn out 9 and a "none". What is none? How can i remove it?

CODE:
i

mport random
        resultat = [random.normalvariate(self.my, self.sigma) for i in range(0,9)] 
        print resultat

[hondros]

http://www.python.org/doc/2.5.2/lib/module-random.html
That is the documentation for the random module. I suggest you take a look at it. Granted, it's not very discriptive of the function you're using, but I don't know what it does either. I think that it generates a float between the two numbers you put in or something. :/ Anyways, what are you using it for? I could give you a better solution using a different function

[vegaseat]

The random.normalvariate( mu, sigma) function has to be called with the arguments:
mu = the requested mean
sigma = the requested standard deviation
You have to supply those arguments.

Also, if you want to loop 10 times use range(10).

Indentations are important with Python. Line up your code properly.

[Gribouillis]

Also, the normal distribution can return negative numbers, there is nothing wrong with that.

[Skrutten]

yeah i know i have loops, and the right indents in my original code. but even if i have a loop the last one turns "none".

what i wonder is, how to make all the numbers positive. there is something wrong with that because i need only positive numbers in my code.

[vegaseat]

yeah i know i have loops, and the right indents in my original code. but even if i have a loop the last one turns "none".

what i wonder is, how to make all the numbers positive. there is something wrong with that because i need only positive numbers in my code.

Use function abs() for absolute value.

Something like this example ...

import random

# mean mu
mu = 12.5
# standard diviation sigma = mu ** 0.5
sigma = 3.53
resultat = [abs(random.normalvariate(mu, sigma)) for i in range(10)]

print resultat

"""my test resultat -->
[7.091583185794657, 3.4583670333483294, 11.877525423436163, 
4.8899955831160469, 12.763448492282313, 13.44488190820579, 
14.050995227925315, 14.896283137343586, 13.475151825413349, 
15.062250014411603]
"""

[Gribouillis]

The probability that normalvariate returns a negative number can be computed with the scipy module like this

from scipy.special import erf as erf
from math import sqrt
sqrt2 = sqrt(2.0)

def proba_negative(mu, sigma):
     return 0.5 * ( 1.0 + erf(- mu/(sigma * sqrt2)))

[Skrutten]

Ah thank you!

I also found that i could use "fabs". What is the difference between abs and "fabs"?

[vegaseat]

Ah thank you!

I also found that i could use "fabs". What is the difference between abs and "fabs"?

abs() is a built-in function and returns an integer or float, dep. on arg. type.
fabs() is part of the math module and returns a float.

For example ...

import math

print abs(-2)        # 2
print math.fabs(-2)  # 2.0

print abs(-123.456)  # 123.456