I am using
rand(200)
in my Rails application.
When I run it in console it always returns random number, but if I use it in application line:
index = rand(200)
index is always the same number.
Why is that and how to overcome this?
Simple pseudo-random number generators actually generate a fixed sequence of numbers. The particular sequence you get is determined by the initial "seed" value. My suspicion is that you are always getting the first number in the same sequence. Therefore I suggest we try to change the sequence by calling srand every time before calling rand, thus changing the seed value every time. The docs explain that, when called without a parameter, srand generates a new seed based on current circumstances (e.g. the time on the clock). Thus you should get a difference sequence and hence a different random number:
srand
rand(200)
Now, you may ask - why are you always getting the same sequence? I have no idea! As someone else suggested in one of the comments, the behavior you are seeing is the behavior one would expect if you had other code, anywhere, that calls srand with the same, fixed value every time. So it might be good to look for that.
Try Random.rand(). For example
Random.rand(200)
Or if you're working with an array you could use sample.
[*1..200].sample
rand(200) is run once and that value is assigned to your index variable. So 'index' will always be that number.
If you want index to change, you will need to continually run rand on it.
Here's a simple way to do that:
def randomIndex(num)
index = rand(num)
return index
end
randomIndex(200)
=> // this value will change
Related
I have this script on 2 npcs but both choose the same random number (7) how do I make the Npcs choose their own number? I did try with self.math.random and it gave an error
so what would the solution be? will I have to create different variables for each npc related to the random function?
function Behavior:Awake()
math.randomseed (os.time())
self.destino = math.random( 1, 7 )
In the engine I work with it says to put self. for independence...
The fact that you call math.randomseed inside a function suggests to me that you're calling it every time you want a random number. The purpose of math.randomseed is to initialize the RNG, which means you're initializing the RNG multiple times, hence the repetition. Usually, you need to call math.randomseed exactly once in the entire program.
it says to put self. for independence...
That's not a great explanation of how self works. self is a function parameter that gets automatically declared when you declare a function with colon notation.
Let's put it via an intuitive example.
I don't want others to modify my source code, so I put a statement in my code:
if( hash_value_of(this_file) != "A_PRE-DEFINED_HASH_VALUE" )
output("Aha! You modified my file!")
So in this case, the pre-defined hash value will affect the actual hash value of the source file at the output stage. It's like a strange loop so that I have to find a way to calculate a hash value beforehand that exactly matches the output.
It is of note that actually I don't care if this method can protect my source file at all. It is just an example. What of concern is how to calculate such a hash value beforehand.
Is there any algorithm matches the need? I am not expecting to get answers like "why do you even think about it?", "what's the usage?". It's only an algorithm discussion. Thanks for any contribution!
I'm looking to integrate a function I am building, but the function would change each iteration based on a given input. For instance:
y=4e^(mx/4)
I would want to integrate with respect to x with a lower and upper bound, but the value of m would change. I know all my values of m.
Can I work with this? My initial assumption would be to use QROMB but that seems limited and unable to handle my issue.
QROMB (and other integrators) want a function of one variable, so you have to get the m in there through the back door. One way is with a common block:
function integrand,x
common int_common,int_m
return,4*exp(int_m*x/4)
end
function integrator,m,xlow,xhigh
common int_common,int_m
int_m=m
return,qromb('integrand',xlow,xhigh)
end
integrator(m,xlow,xhigh) will return the integral you want.
I have this parameter as an array. The array is big, 100 cells. It is a parameter that can be initiated in omnet.ini file. The cells with even numbers should get value A and odd numbers should get value B. How can I do this in an automated manner?
Is there a way besides having all odd and even indices initiated one by one manually?
Wildcards can be useful but I do not know how to use them to separate odd and even indices.
Thanks.
You can access the actual module index with the index operator. Combining this with the conditional operator ?: you can easily define the value:
**.myModule[*].myParameter = index % 2 == 0 ? "A" : "B"
I'm not aware of any feature like this. There are a number of work-arounds you could use:
Provide two parameters and select the correct one in code
Use the volatile keyword (probably not appropriate here)
Put the entire thing in your .ini file
I'd personally implement the first approach, that way you can use the wildcard to pass both parameters ([*].myNode.parameterEven and [*].myNode.parameterUneven) and then set the correct values in your array in a for loop.
However, you could also use the volatile keyword in your NED file, see the manual for more details. However, this approach mostly works well if you have different parameters depending on which node you are assigning it to. For this case I think the first approach is better.
The last alternative is just putting the entire thing in your .ini file, which may be useful if you want to parameterize the array later.
I'm writing an algorithm that detects clones in source code. E.g. if there is a block like:
for(int i = o; i <5; i++){
doSomething(abc);
}
...and if this block is repeated somewhere else in the source code it will be detected as a clone. The method I am using at the moment is to create hashes for lines/blocks and compare them with hashes of other lines/blocks in the same source to see if there are any matches.
Now, if the same block as above was to be repeated somewhere with only the argument of doSomething different, it would not be detected as a clone even though it would appear very much like a clone to you and me. My algorithm detects exact matches but doesn't detect matching blocks where only the argument is different.
Could anyone suggest any ways of getting around this issue? Thanks!
Here's a super-simple way, which might go too far in erasing information (i.e., might produce too many false positives): replace every identifier that isn't a keyword with some fixed name. So you'd get
for (int DUMMY = DUMMY; DUMMY<5; DUMMY++) {
DUMMY(DUMMY);
}
(assuming you really meant o rather than 0 in the initialization part of the for-loop).
If you get a huge number of false positives with this, you could then post-process them by, for instance, looking to see what fraction of the DUMMYs actually correspond to the same identifier in both halves of the match, or at least to identifiers that are consistent between the two.
To do much better you'll probably need to parse the code to some extent. That would be a lot more work.
Well if you're going todo something else then you're going to have to parse to code at least a bit. For example you could detect methods and then ignore the method arguments in your hash. Anyway I think it's always true that you need your program to understand the code better than 'just text blocks', and that might get awefuly complicated.