×
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.

(OP)
If a variable has been defined numerically.  How can it be released for subsequent reuse symbolically?

Of coarse the variable can be reassigned, but how can it be deassigned?

### RE: Reset variables in MathCAD

Sometimes, that works, sometimes, it doesn't.

However, I'm not fully convinced there's a real need to "reuse" a variable name.  If it's going into the same calculation, then some sort of indexed variable should be used.  If it's going into another equation, then a new name should be picked.  Even if you can deassign a variable, the usage of the same name implies that the variable is being reused, as is, since the reader might not even notice the deassignment.

### RE: Reset variables in MathCAD

Some times you want to 'de-assign' a variable so that the symbolic processor will use the variable name, rather than its defined value.
[actually what is happening is that it becomes a self recursive definition]
e.g. if r:=5 and then we define area:=pi*r^2 we can ask the value of area=xx.x but we can't easily ask for the symbolic differential because mathcad will think that all the values are fixed so the differential is zero.

If we insert an r:=r then the symbolic engine will know to stop at the recursion and give d/dr(area) -> 2*pi*r

Further, you can pre assign the result to a function
circ(r):= d/dr(area) -> 2*pi*r

If later you update the formula for area, the follow on equations will live update as well, and you will be able to use the default numeric value that was already in place for r [i.e. the r=5 above].

It just takes a little care to make it look neat sometimes. e.g. place the r:=r just across the right margin for a pretty print

Philip

#### 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!