This commit is contained in:
Trygve 2024-02-27 10:31:50 +01:00
parent 85597c99a5
commit 34f9986a54
3 changed files with 151 additions and 0 deletions

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#include <cstdlib>
#include <iomanip>
#include <iostream>
#include "chain-random-walk.h"
using namespace crw;
namespace {
// set each element forward or backward by 1, at random
void stochastic_unit_step(long size, float config[])
{
for(long i = 0; i < size; i++)
if(std::rand() % 2 == 0) config[i]++;
else config[i]--;
}
void shift_centre_to_origin(long size, float config[])
{
double sum = 0.0;
for(long i = 0; i < size; i++) sum += config[i];
for(long i = 0; i < size; i++) config[i] -= sum/size;
}
const int el_out_max = 9; // show at most the first nine elements
}
float crw::elongation(long size, float config[])
{
float min = config[0];
float max = config[0];
for(long i = 1; i < size; i++)
if(config[i] > max) max = config[i];
else if(config[i] < min) min = config[i];
return max - min;
}
float* crw::step(long size, float previous[])
{
// allocate the next configuration
float* config = new float[size]();
// first, let the chain contract: each element is attracted by its neighbours
for(long i = 0; i < size; i++)
config[i] = 0.5*previous[i] + 0.25*previous[(i-1) % size]
+ 0.25*previous[(i+1) % size];
stochastic_unit_step(size, config); // actual random walk step
shift_centre_to_origin(size, config); // shift such that the average remains zero
return config;
}
void crw::output(long no, long size, float present[], float extreme[], double avg_el)
{
/* output statistics over the run so far
*/
std::cout << std::setw(12) << no << "\t" << std::setprecision(3) << std::fixed
<< std::setw(6) << elongation(size, present) << " "
<< std::setprecision(7) << std::setw(10) << avg_el << " " << std::setprecision(5)
<< std::setw(9) << elongation(size, extreme) << std::setprecision(3) << "\t\t";
/* display the present configuration, showing up to <el_out_max> element coordinates */
for(long i = 0; (i < size) && (i < el_out_max); i++)
std::cout << std::setw(7) << present[i] << " ";
if(size > el_out_max) std::cout << "...";
std::cout << "\t\t";
/* display the most extreme configuration so far,
* showing up to <el_out_max> element coordinates
*/
for(long i = 0; (i < size) && (i < el_out_max); i++)
std::cout << std::setw(7) << extreme[i] << " ";
if(size > el_out_max) std::cout << "...";
std::cout << "\n";
}

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#ifndef CHAIN_RANDOM_WALK_H
#define CHAIN_RANDOM_WALK_H
namespace crw
{
float elongation(long size, float config[]);
float* step(long size, float previous[]);
void output(long no, long size, float present[], float extreme[], double avg_el);
}
#endif

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lab_2/12/memleak.cpp Normal file
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#include <cassert>
#include <cstdlib>
#include <ctime>
#include "chain-random-walk.h"
namespace {
constexpr int default_size = 7;
constexpr int default_steps = 100000000;
constexpr int outlines = 25;
}
/* first argument: array size
* second argument: number of steps
*/
int main(int argc, char** argv)
{
long size = default_size;
if(argc > 1) size = std::atol(argv[1]);
assert(size > 0);
long steps = default_steps;
if(argc > 2) steps = std::atol(argv[2]);
assert(steps > 0);
long outfreq = steps / outlines;
if(outfreq < 1) outfreq = 1;
/* the configuration is given by an array of float numbers */
float* present_configuration = new float[size]();
/* store the one with greatest deviation between min and max element */
float* extreme_configuration = present_configuration;
float extreme_elongation = 0.0;
double el_sum = 0.0;
double el_avg = 0.0;
std::srand(std::time(nullptr)); // initialize the random number generator
for(long i = 0; i < steps; i++)
{
if(i % outfreq == 0)
crw::output(i, size, present_configuration, extreme_configuration, el_avg);
/* here we are calling the random walk step;
* this returns a new configuration (float array) on the heap
*/
present_configuration = crw::step(size, present_configuration);
float present_elongation = crw::elongation(size, present_configuration);
if(present_elongation > extreme_elongation)
{
extreme_configuration = present_configuration;
extreme_elongation = present_elongation;
}
el_sum += present_elongation;
el_avg = el_sum / (i + 1.0);
}
crw::output(steps, size, present_configuration, extreme_configuration, el_avg);
delete[] present_configuration;
}