Produce negative values with a random number generator
Author
Is there a random number generator function that will produce negative as well as positive values.
Rand() apparently does not. Clearly I can do a work around for this, but I'm curious if a function exist to perform this operation. I am sure there is something
Yes, there are. If you mention which programming language you are using, we might be able to direct you to some.
A random number between -10 and 10:
25 random numbers between -10 and 10:
#include <iostream>#include <ctime>#include <boost/random.hpp>int main(){ boost::mt19937 engine(time(0)); boost::uniform_int<int> dist(-10, 10); std::cout << dist(engine);}25 random numbers between -10 and 10:
#include <algorithm>#include <iostream>#include <ctime>#include <boost/bind.hpp>#include <boost/random.hpp>int main(){ boost::mt19937 engine(time(0)); boost::uniform_int<int> dist(-10, 10); std::generate_n(std::ostream_iterator<int>(std::cout, "\n"), 25, boost::bind(dist, engine));}
True rand does not produce negative values but you can adjust it to .
int max = 10;
rand() % max/2 - max/2;
produces values from -5 to 5
int max = 10;
rand() % max/2 - max/2;
produces values from -5 to 5
Quote:Original post by tnutty
int max = 10;
rand() % max/2 - max/2;
produces values from -5 to 5
More like rand() % (max+1) - (max/2).
Author
I tried this rand() % (Max+1) - (Max/2) +.01, but it doesn't seem to produce any negative values.
Also, is there any way that I can make Max a float less than 1 and still have the program work?
Also, is there any way that I can make Max a float less than 1 and still have the program work?
0 to -x: -(rand() % (x + 1))
-x to x: (rand() % (-x - x - 1)) - x
-x to y: (rand() % (-y - x - 1)) - x
-x to -y: -((rand() % (y - x + 1)) + x)
Hopefully that'll help.
-x to x: (rand() % (-x - x - 1)) - x
-x to y: (rand() % (-y - x - 1)) - x
-x to -y: -((rand() % (y - x + 1)) + x)
Hopefully that'll help.
Quote:Original post by zoner7
Also, is there any way that I can make Max a float less than 1 and still have the program work?
Oh, you want real numbers. Just use a different distribution.
#include <algorithm>#include <iostream>#include <ctime>#include <boost/bind.hpp>#include <boost/random.hpp>int main(){ boost::mt19937 engine(time(0)); boost::uniform_real<double> dist(-1.0, 1.0); std::generate_n(std::ostream_iterator<double>(std::cout, "\n"), 25, boost::bind(dist, engine));}And if you insist on using the deprecated rand() function:
double x = double(rand()) / RAND_MAX; // random number between 0.0 and 1.0x = 2.0*x - 1.0; // random number between -1.0 and +1.0Oh and if you want numbers between -1.0 inclusive and +1.0 exclusive, use
double x = rand() / (RAND_MAX + 1.0);x = 2.0*x - 1.0;[Edited by - DevFred on July 24, 2009 7:51:09 PM]
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