×
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.

# How to solve a equation system with more constraints than unkwons?

## How to solve a equation system with more constraints than unkwons?

(OP)
I'm using mathcad to solve an equation system with Given and find.

I had 10 variables (or unkwon values) and 10 equations. My call to find was with 10 parameters.

The problem I'm facing now is that I found the real value for 1 of those 10 variables and now I don't know what equations to remove.

With that known value, I can use one of the equations to find another value and thus, I have 2 known values. I remove that equation but nowI have to remove one more because I have 9 equations for 8 unkowns.

The problem is that when I remove equations 4, 5, 6, 7, 8, 9 or 10 then I get an error about unkown variables not defined or I get not real values but when I remove equation 2 or 3, I get real values but very different.

How can I choose the equation to remove or use more equations than unkown values?

### RE: How to solve a equation system with more constraints than unkwons?

Why are you removing any equations? All this means is that you have 10 equations and 9 unknowns, which is not a serious problem. However, you may want to use Minerr() rather than Find, in case the solution that you think you already have is overly constraining.

### RE: How to solve a equation system with more constraints than unkwons?

(OP)
I wanted to remove equations because Find needs 1 constraint for each unknown or that's what I think.

I just tried to use Minerr with 10 constraints and 9 unknowns the values I get for 6 of those unkowns are extremely dependent on the initial value and the answer is not close to what I think it should be.

When using Find with 10 constraints and 9 unknowns I get an error.

### RE: How to solve a equation system with more constraints than unkwons?

I suggest that you review your equations to make sure that there is actually a solution.

#### 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!