×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Exponential growth curve-fitting

## Exponential growth curve-fitting

(OP)
Hi, i have got a bunch of data points, which i want a curve fitted to. The function for the curve is y= b*a^x . Now, i have tried genfit and expfit, but they find coeffs for y=a*e^(b*x) and y=b*x^b. How do get the coeffs for y= b*a^x?

### RE: Exponential growth curve-fitting

I think genfit works.  Can you list the elements of your function vector?

### RE: Exponential growth curve-fitting

(OP)
well i didnt really know what elements to put in, can u help?

### RE: Exponential growth curve-fitting

The first element of the function vector is the form of your solution:  u1*u2^x,  where u1 and u2 are two elemnts of an array

The second element is the first derivative of the first element with respect to the first variable:  u2^x

The third element is the first derivative of the first element with respect to the second variable:  u1*x*u2^x-1

Here's how the function vector looks.  I included the "[" below as that's what you type to get the subscript.  The "T" at the end denotes a transposed array.

F(x,u)=(u[1*(u[2)^x   (u[2)^x    u[1*x*(u[2)^x-1))T
p=genfit(vx,vy,g2,F)
vx and vy are your data point vectors
g2 is a two element guess

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!