Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hi guys,
    So I'm doing a project on modelling the spread of Ebola. My task is to model a graph to fit the number of cases and deaths in various countries, however I have to find the function on paper, as my teacher said it is too easy using the computer.
    I have decided the graph is exponential in nature, and will try and use the function in the form ae^bx +c.
    If I have the data on a graphing program, how do I find the values of a and b? My teacher said to use the average x value to find the stretch value, but from there on I'm stuck.
    So, how do I find the a and b coefficients from a set of data?
    Thanks
    • Community Assistant
    Offline

    13
    ReputationRep:
    Community Assistant
    (Original post by samiito)
    Hi guys,
    So I'm doing a project on modelling the spread of Ebola. My task is to model a graph to fit the number of cases and deaths in various countries, however I have to find the function on paper, as my teacher said it is too easy using the computer.
    I have decided the graph is exponential in nature, and will try and use the function in the form ae^bx +c.
    If I have the data on a graphing program, how do I find the values of a and b? My teacher said to use the average x value to find the stretch value, but from there on I'm stuck.
    So, how do I find the a and b coefficients from a set of data?
    Thanks
    If you have y=ae^(bx)+c and set x=0 then the value of the y-intercept will be equal to a+c (rearrange for a). Now pick two points on the graph and solve simultaneously for b.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by SherlockHolmes)
    If you have y=ae^(bx)+c and set x=0 then the value of the y-intercept will be equal to a+c (rearrange for a). Now pick two points on the graph and solve simultaneously for b.
    Thank you for this.
    If I wanted to make my model as accurate as possible, would it be best to pick the largest and smallest x values?
    • Community Assistant
    Offline

    13
    ReputationRep:
    Community Assistant
    (Original post by samiito)
    Thank you for this.
    If I wanted to make my model as accurate as possible, would it be best to pick the largest and smallest x values?
    It would probably be best to find multiple values of b and then calculate an average.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by SherlockHolmes)
    It would probably be best to find multiple values of b and then calculate an average.
    Ok, thank you.
    when you said previously to set x=0, do I have to set it to 0? Also, I don't see how I can isolate either a or c as they are both unknowns.
    • Community Assistant
    Offline

    13
    ReputationRep:
    Community Assistant
    (Original post by samiito)
    Ok, thank you.
    when you said previously to set x=0, do I have to set it to 0? Also, I don't see how I can isolate either a or c as they are both unknowns.
    Actually, I don't think it is possible with my method. You have three unknowns a,b,c but can't get 3 equations.
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.