//Classic 2nd order nonlinear ordinary differential equation I64 mp_not_done_flags; #define OX 10 #define OY GR_HEIGHT/2-FONT_HEIGHT #define MICRO_STEP 0.000001 class State { F64 wabbits,hawks, d_wabbits,d_hawks; //Technically, these are not part of the state. }; U0 Steps(State *s) { I64 i; for (i=0;i<10000;i++) { s->d_wabbits=s->wabbits*(1.0-0.10*s->hawks); s->d_hawks =-s->hawks *(1.0-0.01*s->wabbits); s->hawks +=s->d_hawks *MICRO_STEP; s->wabbits+=s->d_wabbits*MICRO_STEP; } } U0 PlotTrajectory(CTask *parent) { I64 i; CDC *dc=DCAlias(,parent); State s; MemSet(&s,0,sizeof(State)); s.wabbits=RandU16%100 +10; s.hawks =RandU16%10 +1; for (i=0;i<1000;i++) { dc->color=LTGREEN; GrPlot(dc,s.wabbits+OX,OY-s.d_wabbits); dc->color=LTRED; GrPlot(dc,s.hawks +OX,OY-s.d_hawks); Steps(&s); } DCDel(dc); LBtr(&mp_not_done_flags,Gs->num); } U0 PredatorPrey() { I64 i; CDC *dc=DCAlias; PopUpOk("This will plot multiple predator-prey\n" "trajectories. It restarts many times\n" "with different, random, initial populations.\n"); SettingsPush; //See SettingsPush try { AutoComplete; WinBorder; WinMax; DocClear; Refresh; dc->color=BLACK; GrLine(dc,OX,0,OX,GR_HEIGHT-FONT_HEIGHT-1); GrLine(dc,0,OY,GR_WIDTH-1,OY); while (!ScanChar) { mp_not_done_flags=1<<mp_cnt-1; for (i=0;i<mp_cnt;i++) JobQue(&PlotTrajectory,Fs,i); do Yield; while (mp_not_done_flags); } } catch PutExcept; SettingsPop; DCFill(dc); DCDel(dc); } PredatorPrey;