# Ising Benchmark

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globals [ result sum-of-spins ;; sum of all the spins -- keeping track of this ;; means that we can always instantly calculate ;; the magnetization (which is the average spin) ] patches-own [ spin ;; holds -1 or 1 ] to benchmark random-seed 2929 reset-timer setup 0 repeat 2000000 [ go ] set result timer end to setup [initial-magnetization] ca ask patches [ ifelse initial-magnetization = 0 [ set spin one-of [-1 1] ] [ set spin initial-magnetization ] recolor ] set sum-of-spins sum [spin] of patches setup-plot update-plot end to go ask one-of patches [ update ] tick update-plot end to update ;; patch procedure ;; flipping changes the sign on our energy, so the difference in energy ;; if we flip is -2 times our current energy let Ediff 2 * spin * sum [spin] of neighbors4 if (Ediff <= 0) or (temperature > 0 and (random-float 1.0 < exp ((- Ediff) / temperature))) [ flip ] end to flip ;; patch procedure set spin (- spin) set sum-of-spins sum-of-spins + 2 * spin recolor end to recolor ;; patch procedure ifelse spin = 1 [ set pcolor red ] [ set pcolor blue ] end to-report magnetization report sum-of-spins / count patches end ;;; plotting procedures to setup-plot set-current-plot "Magnetization" ;; draw a horizontal line to show the x axis set-current-plot-pen "axis" auto-plot-off plotxy 0 0 plotxy 1000000000 0 auto-plot-on end ;; in the real model this isn't a separate procedure and we don't ;; bother calling set-current-plot and set-current-plot-pen all the ;; time. but I've left this in here so the model functions partly as ;; a benchmark on set-current-plot and set-current-plot-pen (and on ;; function call overhead) to update-plot set-current-plot "Magnetization" set-current-plot-pen "average spin" plotxy ticks magnetization end

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