×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • 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.

Students Click Here

solve block question

solve block question

solve block question

(OP)
When solving a system of simultaneous equations, do the variables need to be unitless?

I have a system of six equations with six unknowns in a solve block.  At the end of the solve block {i.e. find u,v,w,x,y,z) = }One of the arguments highlights and I get an error message that says "The units in this expression do not match those of the others in the list".    

RE: solve block question

They don't have to be unitless, but Mathcad, to date, does not allow mixed units in a matrix.  

If you are returning more than 1 variable from a Find(), then it'll wind up in a matrix at the output, where the units must all be the same.

TTFN

RE: solve block question

(OP)
Thanks for the reply.  Since the variables I wish to solve for do not have the same units, is there a clever work around to get the solve block to work or do I need to adjust the equations so that they are dimensionless?

Steve

RE: solve block question

I'm curious, and I could kick myself when I see the answer, but is there a real physical situation where you would have mixed units in a matrix?

I can see some problems with matrix multiplication, for example, if units are not consistent in each matrix.

Unless of course your matrix is actually just a big table or array of numbers treated as one block for convenient indexing.

Bung
Life is non-linear...

RE: solve block question

Tanfolio,

AFAIK, that's about the only way, i.e., normalizing the units


Bung,

AFAIK, there's no obvious physical problem with that sort of solution.  It's basically an artifact of the way Mathcad outputs results from a Solve block and a limitation that Mathcad imposed on arrays.

TTFN

RE: solve block question

A real case I can think of is when describing a 6dof rigid body say, where the natural units are length and number for the x and rx components respectively.

Cheers

Greg Locock

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.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


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
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close