Thread: Exponential and logarithmic graphs/functions HELP

Hi.
I have a maths assignment due in 3 days and i have run into trouble half way through. The basic run down of the assignment is that we have to create an exponential function (with a limit (+c)) from real life data (world record times for triple jump going back 50 years). We are required to convert the data using natural log (ln) to produce a linear graph in which taking that gradient, using it to form an exponential graph.

The data if a regression line is run through them (in excel), forms a line following y=(-a)e^(-bx) whilst the equation found using the ln route gives an equation following y=(a)e^(bx). At this point, there still is no limit thus no asymptote (which is required).

I am having trouble revising the equation still using the ln step (because its required) to form to y=(-a)e^(-bx).

Attached is a .doc of my assignment (the .xls is my working sheet)

Can someone tell me what im doing wrong? The assignment is due on Monday (18/8/08) and i would really appreciated if someone could help me before then.


Thanks.

Perhaps you have not understaood exactly what "Exponential Function" means. It may not mean the most basic y = ae^(bx). Take a look at the Logistic Curve and see what you think.

here's a good link that may be exactly what you need.

Logistic Curve Fitting

sorry i havent replied in a while. I've just come down with the flu (really bad timing for it too...).

The reason i stick with y = (a)e^(bx) is because thats what our teacher expects it to be. He pretty much told us if it does not follow along those lines, its not right...

so yeh... im having trouble sticking to that formula to get a model which fits the data relatively well.