×
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.

# Form of polynomials produced by regress

## Form of polynomials produced by regress

(OP)
Hello everyone, I trying to fit a function to some data I have. I have 3 independent variable so the equation will be of the form f(x,y,z). Using the Regress interp functions I have created the wanted equation and the accuracy is good enough. My problem is that I need to present this equation. I know that the coefficients are in the outcome of the regress function (after the first three) but given that my polynomial is of 8th or 9th degree there are a couple of hundred coefficients ( but not a perfect cube which would make sense to me). So I will need to present my equation as a sum, but I don't know how the form of the created polynomial to write it as a sum. Anyone know anything about the forms of polynomials created by regress?
Thank you all for your help.

### RE: Form of polynomials produced by regress

You are assuming that a general polynomial will approximate the function as a result of one variable.
I have found that there is a practical order to the degree of polynomial that makes sense.
x0+x1*x+x2*x^2+x3*x^3...
Y0+y1*y+y2*y^2+y3*y^3...
z0+z1*z+z2*z^2+z3*z^3...
and multiply them together. This is easy in Mathcad.

We don't know the range of each variable. Knowing that would help or even getting a clue as to what you are really doing would help.
It could be a different type of polynomial is required for each direction. One could try Pade approximants too.

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
http://forum.deltamotion.com/
IFPE Hall of Fame Member

#### 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.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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!