rces,pletewithwarningsigns,workprotectionfacilities2.2 相轨线分析s0≤1σ,则i(t)单调减小至0,s(t)单调减小至s∞.ofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilities在数值计算和图形观察的基础上,利用相轨线可以看出,如果仅当患者比例i(t)有一段增长ofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilities讨论解i(t),s(t)的性质:i~s平面称为相平面,相轨线在相平面的定义的时期才认为传染病在蔓延,那么1σ是一个阈值,ofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilities域(s,i)∈D为D={(s,i)|s≥0,i≥0,s+i≤1},当s0>1σ时传染病就会蔓延.而减小传染期接触数28. i=(s0+i0)-s+(3)σ(s0+i0)-s∞+1ln在0,σ内的根,在图形上s∞是相轨线与s轴在σ内交点的横坐标,此例中s∞约为0.85.(3)若s0>1,则i(t)先增加,当s=1时,i(t)1(ofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilitiesofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilitiesofruraldrinkingwatersources,pletewithwarningsigns,workprotectionfacilities
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