mrcotton said:
mrcotton said:
When you call srand(seed), you are giving it the seed. Because you have not set seed to another value, seed is 0 in every run, and your call is always the same as seed(0). So your following calls to rand gave you the random number series associated with a seed of 0. Try something like "call srand(7873)". 7873 is just a prime number I grabbed without knowing if it is a good one. It's probably ok. If you want a different series of random numbers for each run, I think you can skip the call to srand and it will use the program start time to generate it's own seed and the series generated will be different each time.mrcotton said:
mrcotton said:
mathman said:
mrcotton said:
$r_min = 0.5;
$r_max = 2;
$r_min2=$r_min**2;
$r_max2=$r_max**2;
foreach $i (0..100000000){
# calculate uniform random between the squares of the upper and lower limits
$unif = ($r_max2 -$r_min2)*rand() +$r_min2;
# take the square root for the final random radious
$rand_radius = $unif**0.5;
# record results in a histogram for every 0.1 radius increment
&record_hist;
}
... record, scale and print resultsHistogram results
min r max r count Scaled Scaled ~ 1/r
count
0.500 0.600 2934512 1.000 1.000
0.600 0.700 3464278 1.181 0.999
0.700 0.800 3999929 1.363 1.000
0.800 0.900 4532096 1.544 0.999
0.900 1.000 5068879 1.727 1.000
1.000 1.100 5601693 1.909 1.000
1.100 1.200 6133230 2.090 1.000
1.200 1.300 6667574 2.272 1.000
1.300 1.400 7204386 2.455 1.000
1.400 1.500 7727856 2.633 0.999
1.500 1.600 8267815 2.817 1.000
1.600 1.700 8804165 3.000 1.000
1.700 1.800 9333855 3.181 1.000
1.800 1.900 9864373 3.362 0.999
1.900 2.000 10395360 3.542 0.999mrcotton said:
mrcotton said:
@jtbell is right. I didn't want the bookkeeping to distract from the essential point. Here is the omitted code at the end of the program:mrcotton said:
sub record_hist {
# record results in a histogram for every 0.1 radius increment
$hist_index = int(10*$rand_radius);
$hist[$hist_index]++;
}
# print the histogram results between the original radius limits
print <<END;
Histogram results
min r max r count Scaled Scaled ~ 1/r
count
END
foreach $i (5..19){
# histogram cell range of radius
$hist_lower = $i/10;
$hist_upper = ($i+1)/10;
# scale raw numbers versus cell for least radius (should grow proportional to radius)
$scaled_to_first_cell = $hist[$i]/$hist[5];
# scale again versus inverse of middle radius of the cell (should be 1.0)
$scaled_to_inverse_radius = $scaled_to_first_cell * ( 0.55/($hist_lower+0.05));
printf "%6.3f %6.3f %8d %6.3f %6.3f\n",
$hist_lower,
$hist_upper,
$hist[$i],
$scaled_to_first_cell,
$scaled_to_inverse_radius;
}// DEFINE canvas size
int xsize=400;
int ysize=400;
// COMPUTE center of canvas
int xhalf=xsize/2;
int yhalf=ysize/2;
// DEFINE inner and outer radii
float rinner=50;
float router=200;
// DEFINE number of random dots to draw
int NDOTS=100;
int dots=0;
void setup() {
// DEFINE a xsize pixels x ysize pixels canvas
size(xsize,ysize);
// DRAW outer circle with diameter 2*router pixels
ellipse (xhalf,yhalf,2*router,2*router);
// DRAW inner circle with diameter 2*rinner pixels and fill in as light GRAY
fill(200,200,200);
ellipse(xhalf,yhalf,2*rinner,2*rinner);
}
void draw() {
// DRAW no more than NDOTS
if(dots<NDOTS) dots++; else return;
// COMPUTE polar position of random dot
float r = (float)(randomWithinRange(rinner,router));
float theta=(float)(randomWithinRange(0.0,2*Math.PI));
//println("r="+r+" theta="+theta);
// COMPUTE x,y position of random dot
float xdot=r*cos(theta)+xhalf;
float ydot=r*sin(theta)+yhalf;
// DRAW a random dot 2 pixel diameter
ellipse(xdot,ydot,2,2);
}
// ===============================================================
// The following method: randomWithinRange(min,max) was copied from this webpage:
//
// http://stackoverflow.com/questions/7961788/math-random-explained
// ===============================================================
// RETURN a random value between two values
double randomWithinRange(double min, double max)
{
double range = Math.abs(max - min);
return (Math.random() * range) + (min <= max ? min : max);
}The purpose of filling a disk with random points in Fortran is to generate a set of random coordinates within a disk shape. This can be useful for simulating random processes or creating randomized data sets for statistical analysis.
This task can be accomplished in Fortran by using the RAND() function to generate random numbers and the SQRT() function to calculate the distance of each point from the center of the disk. A loop can be used to generate multiple random points within the disk.
Yes, the size of the disk can be adjusted in this process by changing the radius value used in the calculation for the distance from the center. This can be a fixed value or a randomly generated value to create disks of varying sizes.
No, there is no set limit to the number of points that can be generated within the disk. However, the more points that are generated, the longer it will take for the program to run.
To ensure that the points are evenly distributed within the disk, you can use a polar coordinate system to generate the points. This will result in a more uniform distribution compared to using a rectangular coordinate system.
