'programming/C_C++'에 해당되는 글 279건

  1. 2017.11.21 random

random

programming/C_C++ 2017. 11. 21. 11:26
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double r;  /* random value in range [0,1) */
double x;  /* random value in range [0,M) */

long int M;  /* user supplied upper boundary */

int y;  /* random integer in range [0,M) if M is an integer then range = [0,M-1] */
int z;  /* random integer in range [1,M+1) if M is an integer then range = [1,M] */

srand(  (unsigned int)time(0) );

r = (   (double)rand() / ((double)(RAND_MAX)+(double)(1)) );

/* r is a random floating point value in the range [0,1) {including 0, not including 1}. Note we must convert rand() and/or RAND_MAX+1 to floating point values to avoid integer division. In addition, Sean Scanlon pointed out the possibility that RAND_MAX may be the largest positive integer the architecture can represent, so (RAND_MAX+1) may result in an overflow, or more likely the value will end up being the largest negative integer the architecture can represent, so to avoid this we convert RAND_MAX and 1 to doubles before adding. */

x = (r * M);

/* x is a random floating point value in the range [0,M) {including 0, not including M}. */

y = (int) x;

/* y is a random integer in the range [0,M) {including 0, not including M}. If M is an integer then the range is [0,M-1] {inclusive} */

z = y + 1;

/* z is a random integer in the range [1,M+1) {including 1, not including M+1}. If M is an integer then the range is [1,M] {inclusive} */


We can combine the above equations to create formulas for r,x,y,z:

r = [0,1) = {r: 0 <= r < 1} real
x = [0,M) = {x: 0 <= x < M} real
y = [0,M) = {y: 0 <= y < M} integer
z = [1,M] = {z: 1 <= z <= M} integer

 


참고 : http://blog.naver.com/baek2187/150035158805

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