Jurpie Posted January 16, 2011 Report Share Posted January 16, 2011 how can you describe "how well your model fits" the data? is it enough to say all the points lie near the the model? Reply Link to post Share on other sites More sharing options...
gldurocher Posted January 16, 2011 Report Share Posted January 16, 2011 how can you describe "how well your model fits" the data? is it enough to say all the points lie near the the model?for that section i would think that you just plot both sets of data on the same graph. yes, no? Reply Link to post Share on other sites More sharing options...
Jurpie Posted January 16, 2011 Report Share Posted January 16, 2011 yea I did that but it is asking to evaluate how WELL the models fit. I'm just wondering if we can simply give an empirical answer, like "it fits the data well" or if we need to do any calculations? :/ Reply Link to post Share on other sites More sharing options...
dessskris Posted January 16, 2011 Report Share Posted January 16, 2011 how can you describe "how well your model fits" the data? is it enough to say all the points lie near the the model?I have no experience with type II IA's yet but if I were to do this task, for that part I would say something like: the data points fit the curve well even though point (X, Y) does not fit the curve that well and the curve should plateau off at the end. Something like that, really. Just like describing graphs in Science And yes as gldurocher said, don't forget to plot the function and the data set on the same set of axes 1 Reply Link to post Share on other sites More sharing options...
Jake16JA Posted January 17, 2011 Report Share Posted January 17, 2011 How do I go about starting a type 2 IA like this? Should I just jump right in with the first question about the relevant variables and parameters, or should I find some background information about the population in China during this 58 year period? When it says analytically develop one method, should I do all the calculations for finding the regression I preformed on my graphing calculator, or say I used technology to find a model that fits the data?IB is a new program in my school, and I'm a part of the first IB class, so my teachers are just as clueless as me. Reply Link to post Share on other sites More sharing options...
jdbrooks Posted January 17, 2011 Report Share Posted January 17, 2011 How do I go about starting a type 2 IA like this? Should I just jump right in with the first question about the relevant variables and parameters, or should I find some background information about the population in China during this 58 year period? When it says analytically develop one method, should I do all the calculations for finding the regression I preformed on my graphing calculator, or say I used technology to find a model that fits the data?IB is a new program in my school, and I'm a part of the first IB class, so my teachers are just as clueless as me.You need to have an introduction before you jump into any of the stuff that the portfolio asks you to do, and that us where you can put the background information about regression analysis and what not. Try a program such as advanced grapher, it only works for windows computer but it is an excellent tool, and put pictures into your portfolio to show that you used technology. The pictures prove you used technology and you can then reference them and say stuff like based off of the graph etc. I hope this helps, if you have any more questions you can ask me! IB has been around my area and school for a long time so we all know the drill. how can you describe "how well your model fits" the data? is it enough to say all the points lie near the the model?for that section i would think that you just plot both sets of data on the same graph. yes, no?i think my math teacher said something about an R value that is a systematic way that can actually tell you how accurate the graph is to the points.(www.bized.ac.uk/timeweb/crunching/crunch_relate_expl.htm) I hope this helps and the site should explain the R value better than i can Reply Link to post Share on other sites More sharing options...
Manstein Posted January 18, 2011 Report Share Posted January 18, 2011 I'm analytically developing a model based on:At3+Bt2+Ct+554.8 = PAny help on how to solve the three constants A, B and C? Reply Link to post Share on other sites More sharing options...
helenpark Posted January 18, 2011 Report Share Posted January 18, 2011 what are variable and parameter? Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 what are variable and parameter?How long have you been studying math? I can't believe that you don't know what variables are. x and y are examples of variables. There is this formula in Physics world:F=9*109*Q1Q2/r2where F, Q and r are variables and 9*109 is a constant. Being a variable means that its value can be anything, depending on the domain. Let's say Q is an element of Real numbers. Thus, Q can be any real number! It may be -0.9, may be 0, may be √7, may be pi, anything.. That's why it's a variable.Parameters..not really sure either but you may want to read this quote below vI think Parameters can be any numbers.I do not know if you learn this in SL, but let's say you have 3 expressions in which there are 3 variables: x, y and z.Example:2x+2y+z=13x+12y+3z=6x+4y+z=2Solving the above equation by doing RREF, it wil turn out that z is a parameter, z=t given that t is a real number6y+z=3, y=(3-t)/63x+z=0, x=-t/3That means, t can be anything. can be -8, 0, 1.2, 23, 94, etc... and thus the solution of the system is a straight lineIf it's still unclear let me know I will explain it more clearly. Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 I'm analytically developing a model based on:At3+Bt2+Ct+554.8 = PAny help on how to solve the three constants A, B and C?Substitute some sets of values of t and P and solve it using matrices..?Say (t, P) are (1, 2), (2, 3) and (3,4). I am picking random constants btw.Then you will get:A(1)3+B(1)2+C+554.8 = 2A+B+C=-552.8A(2)3+B(2)2+2C+554.8 = 38A+4B+2C=-551.8A(3)3+B(3)2+3C+554.8 = 427A+9B+3C=-550.8So you now have:A+B+C=-552.88A+4B+2C=-551.827A+9B+3C=-550.8Then you can solve it with matrices. I doubt if you learn it in SL but I'll do RREF. Or you can try using substitution or elimination PS: if it was a quadratic function I would find the discriminant to get some expression. idk what we can do with cubic functions though, sorry. 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 How do I go about starting a type 2 IA like this? Should I just jump right in with the first question about the relevant variables and parameters, or should I find some background information about the population in China during this 58 year period? When it says analytically develop one method, should I do all the calculations for finding the regression I preformed on my graphing calculator, or say I used technology to find a model that fits the data?IB is a new program in my school, and I'm a part of the first IB class, so my teachers are just as clueless as me.FYI you may want to read the Math Portfolio Tips..You should start with an intro as described in that ^ thread. Describe briefly what the task is all about. If I were to do this task I'd start with introducing the data given in the task, defining variables and parameters and modelling a function after describing what I will investigate in my portfolio should I find some background information about the population in China during this 58 year period?This is a Mathematics portfolio. No you don't need that. at all.When it says analytically develop one method, should I do all the calculations for finding the regression I preformed on my graphing calculator, or say I used technology to find a model that fits the data?First introduce what type of function you are going to model. Let's say it's a 6th polynomial. Give the general function first, like P=ax6+bx5+cx4+dx3+ex2+fx+gThen you find the values of a, b, c, d, e, f and g mathematically. Show ALL the calculations you perform. If you do this with your GDC, I suggest connecting it to your laptop so you can put a screenshot there in order to prove that you have used technology.In this part, don't find the function with a graphing software yet because right after this part you'll need to do that.And if you have any more questions you can ask ME too! Or just post in this thread so anybody can actually help you. You may ask your friends to join IBS too, or even your teacher, so they can actually get some tips/help with their IA's, okay. Reply Link to post Share on other sites More sharing options...
helenpark Posted January 18, 2011 Report Share Posted January 18, 2011 what are variable and parameter?How long have you been studying math? I can't believe that you don't know what variables are. x and y are examples of variables. There is this formula in Physics world:F=9*109*Q1Q2/r2where F, Q and r are variables and 9*109 is a constant. Being a variable means that its value can be anything, depending on the domain. Let's say Q is an element of Real numbers. Thus, Q can be any real number! It may be -0.9, may be 0, may be √7, may be pi, anything.. That's why it's a variable.Parameters..not really sure either but you may want to read this quote below vI think Parameters can be any numbers.I do not know if you learn this in SL, but let's say you have 3 expressions in which there are 3 variables: x, y and z.Example:2x+2y+z=13x+12y+3z=6x+4y+z=2Solving the above equation by doing RREF, it wil turn out that z is a parameter, z=t given that t is a real number6y+z=3, y=(3-t)/63x+z=0, x=-t/3That means, t can be anything. can be -8, 0, 1.2, 23, 94, etc... and thus the solution of the system is a straight lineIf it's still unclear let me know I will explain it more clearly.then, population and year are variables? Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 then, population and year are variables?Sorry for the late reply.. Yes they definitely are each represented by the letter P and t Reply Link to post Share on other sites More sharing options...
helenpark Posted January 18, 2011 Report Share Posted January 18, 2011 then, population and year are variables?Sorry for the late reply.. Yes they definitely are each represented by the letter P and tso, we can choose anything to represent it? other than P and t?thank you for your help! but i still dont get what parameter is T_T Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 so, we can choose anything to represent it? other than P and t?thank you for your help! but i still dont get what parameter is T_TWell you can. but it is more logical to use P and t because they stand for population and time respectively and anyway on the task paper they put P(t)=function, right? so yeah..Sorry I can't help much with parameter either don't really understand it. I suggest reading http://mathworld.wolfram.com/Parameter.html btw Reply Link to post Share on other sites More sharing options...
gracebolt Posted January 18, 2011 Report Share Posted January 18, 2011 Can anyone explain to me analytically develop a logarithmic function? My teacher taught us about every other function, but not this one. Thanks so much! Reply Link to post Share on other sites More sharing options...
dessskris Posted January 18, 2011 Report Share Posted January 18, 2011 Can anyone explain to me analytically develop a logarithmic function? My teacher taught us about every other function, but not this one. Thanks so much!I think I explained this somewhere in this thread or in another IA thread but anyways..Define the general function. May be y=a+b*ln(x) or even y=a+b*ln(cx+d) but may be harderThen if you choose the first function, substitute 2 sets of values of x and y that you get from the task, which are t and P respectively to find a and b. You will get 2 expressions in terms of a and b which you can solve mathematically.If you choose the second function, substitute 4 sets of values of x and y that you get from the task, which are t and P respectively to find a, b, c and d. You will get 4 expressions in terms of a, b, c and d which you can solve mathematically also.Anything else just ask again 1 Reply Link to post Share on other sites More sharing options...
TJiff94 Posted January 19, 2011 Report Share Posted January 19, 2011 I've figured out what type of function I want to use, but I'm experiencing some extreme difficulties with "analytically" finding the values of a,b, and c in a cubic function. Any ideas on how I could find these values? Reply Link to post Share on other sites More sharing options...
adbhatia Posted January 19, 2011 Report Share Posted January 19, 2011 Can anyone explain how to start the first question of the Portfolio Reply Link to post Share on other sites More sharing options...
helenpark Posted January 19, 2011 Report Share Posted January 19, 2011 do you guys graph the year on y-axis and the population on x-axis? or the other way round? because i graphed the year on the x-axis but the result seems like a straight line and when i did it the other way round, i got a curvy line. please help!I've figured out what type of function I want to use, but I'm experiencing some extreme difficulties with "analytically" finding the values of a,b, and c in a cubic function. Any ideas on how I could find these values? How do you decide which one to use? do you explain what functions you are going to use first on the paper? then finally you decide? is it logistic? Reply Link to post Share on other sites More sharing options...
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