M1AguRstKin0B Posted July 13, 2011 Report Share Posted July 13, 2011 SIGH. (10)(1)1950=10 this expression is correct. use your calculator. 1 to the power of anything is still 1. imagine multiplying 1 by a thousand more of 1s. and so 10x1=10. look, if x is your time and y is the population, you substitute x and y into your general equation! giving something like 103=ab1945. why did you substitute a and x??? how many times do I have to repeat this??? and you don't come up with b that way. you should be able to think creatively and critically. if it's x, it's x. it's not a or b, or y. if your friend told you something, go check it for yourself and see if it's true or not. you're not going to write in the IA "my friend said b is 1 so my equation is this." prove it, mathematically. or you probably should have done studies. I would if I could, Desy. So then. . . In simple terms,this method of mine isn't wrong, but the values I've plugged in them are just wrong(?) And remember about the log function wherein I asked you, since you told me I should solve them Simultaneously, y = a ln(x) + b y = a ln(x) + b like that? wherein y is population and x is time as for the other function, y = abx - reason why I wrongly did what I have done there was because, I never considered Y to be anything but just something to show you are looking for it Anyway, let me repeat what you've explained, y is population x is time a and b are constants in which I think of any values so that when I have say, 554.8=(4)(1)1994 then 554.8 = ANS afterwards, erm, divide both by 554.8 to get the ANS? Yes yes? You know Desy, I have a feeling after this first part of my IA is done, I can soldier onwards to the next 2 since as long as I've got that function of mine, which I can use again - like you've told me - it should be easier for me, right? (or something like that.) Guys, does anyone know if there is like this online version of a TI-89 Titanium calculator(?) - Since I have forgotten mine at home, and i will be away on a 3 day trip, so, yeah. heh heh. Thanks! 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted July 15, 2011 Report Share Posted July 15, 2011 God..... i don't know how else i can explain this to you.........okay I'm giving you an example now!in year 1800, the population was 50in year 1850, the population was 80I want to get a logarithmic function y = a ln(x) + blet y=population and x=timeTHINK LOGICALLY! what equations will you get?50 = a ln(1800) + b80 = a ln(1850) + bnow solve the equations simultaneously for a and bsecond equation - first equation gives:30 = a(ln1850 - ln1800)30 = a[ln(1850/1800)]a = 30/ln(1850/1800)(calculate it with your calculator)then find b...since you are in Math SL and you are in IB1 already, I highly expect you to know how to find b because I swear to God I even learnt this in middle school so...... Reply Link to post Share on other sites More sharing options...
Markee Posted July 16, 2011 Report Share Posted July 16, 2011 Aaaaagh! Now it's my turn to go "This IA is due in 2 days and I really need help!" Basically, you know (if you have a TI 89 Titanium) how your regression(R2) should be displayed along with the general equation? Well. mine isn't doing so. HELP? 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted July 16, 2011 Report Share Posted July 16, 2011 Regression is not R². TI calculators don't display R² value (not sure about the newest TI calculator though). The general equation is only displayed when you put your cursor over the graph (or at least in TI-Nspire this is the case). AFAIK only Excel and Logger Pro display R² value. Reply Link to post Share on other sites More sharing options...
CkyBlue Posted July 16, 2011 Report Share Posted July 16, 2011 Aaaaagh! Now it's my turn to go "This IA is due in 2 days and I really need help!" Basically, you know (if you have a TI 89 Titanium) how your regression(R2) should be displayed along with the general equation? Well. mine isn't doing so. HELP? Hmm... I think I got that to work by turning on the "Diagnostics" on my TI-84 Silver Edition... you should be able to find that... somewhere in your -- idk there was a button for long list of functions to turn on. Sorry, I don't have the GDC since I'm finished with Math now Reply Link to post Share on other sites More sharing options...
Markee Posted July 16, 2011 Report Share Posted July 16, 2011 Regression is not R². TI calculators don't display R² value (not sure about the newest TI calculator though). The general equation is only displayed when you put your cursor over the graph (or at least in TI-Nspire this is the case). AFAIK only Excel and Logger Pro display R² value. B-but it does. It did so with Cubic and Linear so far. I've checked it. What the heck does AFAIK mean? o.o 1 Reply Link to post Share on other sites More sharing options...
Markee Posted July 17, 2011 Report Share Posted July 17, 2011 erm, how can you explain mathematically how well your model fits the graph? O.o I mean, besides your model (i used Quartic) nearly shaping up the original graph as the number of polynomials increases after using the cubic regression, linear regression. 1 Reply Link to post Share on other sites More sharing options...
dessskris Posted July 17, 2011 Report Share Posted July 17, 2011 talk about points that do not fit. talk about the shape of the curve. 1 Reply Link to post Share on other sites More sharing options...
imdroppingibmath Posted July 18, 2011 Report Share Posted July 18, 2011 If you have this IA, you know what I'm talking about. P(t)=K / (1+ L e^(-Mt))how do you find the variables M K and L Reply Link to post Share on other sites More sharing options...
dessskris Posted July 18, 2011 Report Share Posted July 18, 2011 use your GDC to generate a logistic model. from there you can get your K L M. 1 Reply Link to post Share on other sites More sharing options...
CkyBlue Posted July 18, 2011 Report Share Posted July 18, 2011 While plotting the data points that you are given, of course Go logistic regression! Reply Link to post Share on other sites More sharing options...
alecx Posted July 26, 2011 Report Share Posted July 26, 2011 Oic..well you may want to do an analytical approach then if you feel like it. So you have: P = K / (1 + L e-Mt) where K, L, M are parameters. You need to solve for 3 parameters. So you need 3 data points. Just pick from your data! Since I'm giving an example I won't use the original data ok. Let's say we have (5, 10), (10, 20), (15, 30) btw format is (t, P) Substituting those values into the general equation you have: 10 = K / (1 + L e-5M) 20 = K / (1 + L e-10M) 30 = K / (1 + L e-15M) From 1st eq: L e-5M = K/10 - 1 Do the same for the rest and just try to solve idk though I haven't tried that either! If you dare to try but later find some difficulties, reply here and I will try to help This is really useful, thanks! Reply Link to post Share on other sites More sharing options...
mctaco Posted August 23, 2011 Report Share Posted August 23, 2011 I don't know, maybe there is but as far as I remember the instruction specifically tells you to DO it using a technology. so why bother analytically? believe me, there is yet plenty to be done, don't make it even more complicated;)well, i hope that explaining how to use a GDC is not by the rules so here it is:firstly clear all lists from memory(that's not compulsory but my teacher always says to do so)then go to stat, from there to edit and just plug in the data from the table instruction hasthen 2nd quitthen again stat and you have to move to the calc submenu therenow you have a list of functions so just choose one you want and click enteryou will be in the mail window and there should be some function name inserted click 2nd and L1(under1)commaclick 2nd L2(under 2)commago yo vars and submenu y-vars and choose function and then y1enterthat should do the trick:)from there you will manage to SEE the values of K, L and M;)Thankyou times a million. My IA is due tomorrow and you saved me! Reply Link to post Share on other sites More sharing options...
helpme123 Posted August 28, 2011 Report Share Posted August 28, 2011 Hi I used the matrix method proposed by Desy to find a quartic using the rref method and I developed an answer, but when I graph the quartic function it does not appear on the window in my calculator and cover the data points of the population trend, I am confused as to what I have done wrong can anyone help? Thankyou my portfolio is due tomorrow Reply Link to post Share on other sites More sharing options...
dessskris Posted August 28, 2011 Report Share Posted August 28, 2011 really? did you try converting the year to be smaller btw? and substituting it later? if you get something like y=ax⁴+bx³+cx²+dx+e then I faced the same problem. try to convert it, get something like y=a((x-1900)/5)⁴+........ Reply Link to post Share on other sites More sharing options...
helpme123 Posted August 28, 2011 Report Share Posted August 28, 2011 really? did you try converting the year to be smaller btw? and substituting it later? if you get something like y=ax⁴+bx³+cx²+dx+e then I faced the same problem. try to convert it, get something like y=a((x-1900)/5)⁴+........ You are a life saver! I did convert the year to a smaller number like you suggested earlier in the thread but once I found my values I forgot to substitute the ((x-1900)/5) part in and just left it as X, my model now fits most of the points, I could probably try to the the 6th polynomial but I don't have much time left to do the portfolio so I am not sure if I should try. I have just another question I don't really understand this part of the question "What types of functions could model the behaviour of the graph? Explain your choices." what do they mean by explain your choices what should be included? Reply Link to post Share on other sites More sharing options...
dessskris Posted August 28, 2011 Report Share Posted August 28, 2011 yay! glad to hear lol finish it first. if you still have time at the end of the day, try working out the 6th poly. hmmm I'm not very sure but you could try mentioning the features in a quartic function (e.g. 3 stationary points?) that you can find in your data graph. it's just like if your graph is periodic, you will choose sin or cos graphs because of the periods. Reply Link to post Share on other sites More sharing options...
helpme123 Posted August 29, 2011 Report Share Posted August 29, 2011 I am unsure on how to "Comment on how well your model fits the original data" in mathematical terminology does anyone have any advice on how to go about answering such questions? Reply Link to post Share on other sites More sharing options...
dessskris Posted August 29, 2011 Report Share Posted August 29, 2011 you can say something like your graph fits the data points, state how many points do not fit the graph (if any), and you may talk about the shape of the graph that is similar to shape formed by the data points. etc. Reply Link to post Share on other sites More sharing options...
ridaynax Posted September 23, 2011 Report Share Posted September 23, 2011 i have the same portfolio and i am not able to get the k, l , m values .... how do you do it Reply Link to post Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.