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