系統(tǒng)動力學(xué)模型講ppt課件-資料下載頁
2025-05-03 01:32本頁面
【正文】 re detailed graphs when you see something interesting. ? The things to be looking for when you are evaluating behavior are the period of oscillation（振動） , the extent by which variables change and the degree of damping(衰減 ). ? The period of oscillation is the time from one peak to the next on the time graphs. ? Damping is the decrease in amplitude that occurs from peak to peak, where amplitude is the distance along the y axis from the eventual value the variable settles to. ? It should be easy to see that productivity and inventory coverage do not significantly change these while time to adjust workforce and time to correct inventory do. time to adjust workforce e x pe r i m e n tba s e r u nW or kf or c e200150100500n e t h i r e r a t e60300 30 600 25 50 75 100T i m e ( M on t h ) 5） Causal Tracing ? Just as you looked at the causes of Inventory by using the Causes Tree Diagram Analysis tool, you can also look at graphs of behavior of the variables that cause Inventory to change. ? Click on the Reset All button or use the key bination Ctrl+Home. ? Click on Inventory to select it into the workbench. ? Click on the Causes Strip Analysis tool ?A strip graph is generated that shows the Workbench Variable (Inventory) at the top, and all the variables that directly cause Inventory to change below it (production and sales). ?we will look into production and not sales to understand the source of this oscillation. ? Causal Tracing is a quick and powerful tool that helps us determine what portions of a model are causing which types of behavior. ? The Causes and Uses Tree Diagrams and the Table tool can all be used for Causal Tracing but the most monly used tool is the Causes Strip tool and we will use that to investigate the sources of oscillation in this model. ： LOOKUP、 TIME、 STEP ? 1） LOOKUP：說明在一個模擬模型中任意兩個變量之間的函數(shù)關(guān)系；可以描述一個表格包含兩個變量的一組值。 ? 比如，改變原儲蓄存款模型（ SavingInterest）。當存款少于 5000￥，利率為 5％；存款不少于 5000￥，利率為 7％ 。 ? 相當于原來 DYNOMA 中的 table函數(shù) 演示 ? 2） TIME變量 ? 一些 Vensim功能明顯是時間函數(shù)，為了使用這一功能，在模型中必須使用 TIME當作函數(shù)。 ? 比如，對某些產(chǎn)品 100單位振幅與 12個月季節(jié)變化需求。時間以月為單位。 ? Variable Demand=100*sin(2**Time/12) 演示 注意： Time 用 符號包起來，表示它是一個隱藏式變量 V a ri a b l e D e m a n d1000 10 011111111 1111111111111110 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100T i m e ( M on t h )V a r i a bl e D e m a n d : C u r r e n t 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 13） STEP函數(shù) ? 階躍函數(shù)產(chǎn)生一個從零到給定值的一次階躍。 ? 比如 sales=100 + STEP(50,20) ? The STEP function is one of the most monly used input functions. This function returns 0 until Time reaches {stime} and then it returns {sheight}. In our example it will return 0 till time 20 then it will return 50 so that sales will start at 100, remain constant till time 20 and then jump to 150. s a l e s200140801 1 11 1 1 1 1 1 1 1 1 1 1 10 10 20 30 40 50 60 70 80 90 100T i m e ( M on t h )s a l e s : C u r r e n t W i dg e t / M on t h1 1 1 1 1 1 1 1 1Time (Month) sales Time (Month) sales Time (Month) sales 0 100 1 100 21 150 41 150 2 100 22 150 42 150 3 100 23 150 43 150 4 100 24 150 44 150 5 100 25 150 45 150 6 100 26 150 46 150 7 100 27 150 47 150 8 100 28 150 48 150 9 100 29 150 49 150 10 100 30 150 50 150 11 100 31 150 51 150 12 100 32 150 52 150 13 100 33 150 53 150 14 100 34 150 54 150 15 100 35 150 55 150 16 100 36 150 56 150 17 100 37 150 57 150 18 100 38 150 58 150 19 100 39 150 59 150 20 150 40 150 60 150 作業(yè)： ? 《現(xiàn)代地理學(xué)中的數(shù)學(xué)方法》 P370378 ? （要求至少包括正負反饋回路各一個） ? ：《 VensimUsersGuide》P1122； P2340； P75P90
教學(xué)課件相關(guān)推薦
鄂ICP備17016276號-1