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Solve Block

ELSID
4-Participant

Solve Block

The Collabs assistance is greatly appreciated. I need to solve for L.min and I was trying to set up in a solve block. Problem is that L.min is defined within 2 other variables.
7 REPLIES 7
ELSID
4-Participant
(To:ELSID)

Well I got it to work by substituting equations for variables (see attached). It works on MathCAD 14 M030, but I saved as Ver. 11 for greater collab. I still go back to the original sheet. Is there a way of using multiple equations to solve for a value in a solve block?

>Is there a way of using multiple equations to solve for a value in a solve block ?<<br> ______________________

You solve for "a" variable, not for a value. You need as many equating expressions as there are variables to solve [399 in Mathcad 11]. Explore the Mathcad qs.

jmG

Yes, you can use multiple equations in a solve block. But....

In general you have to solve for exactly as many variables as you have equations (vector equations or variables modify this).

All variables used in the solve block must be defined prior to the solve block. Those with known values must be defined with those values, those whose values are not known (are variables for which you are solving) must be defined with guess values.


You have a units problem in the equations for Aw and Pw. You are multiplying Lmin by a foot, but Lmin is already defined as a length.

You have an inexplicable constant of 1ft appearing in various places in the equations. I suspect that that really should be a variable, defining an aspect of the system.

In general where one variable is simply a function of other variables it is better to just make a function definition for it rather than try to implement the relationship as a solve blcok constraint. Remember, = is a predicate and never defines anything. That remains true in a solve block, where it is merely a constraint.
__________________
� � � � Tom Gutman
ELSID
4-Participant
(To:TomGutman)

Tom,
I am attaching a revised worksheet with some parameters. I was going to update what I had when I noticed you replied. Page 2 solves the for L as expected. Pg 3 I could not get to work. Would you be able to show me how you would change the worksheet to "make a function definition for it rather than try to implement the relationship as a solve block constraint"?


__________________
� � � � Tom Gutman
ELSID
4-Participant
(To:TomGutman)

Thank you. I am still having a hard time "seeing" and working with functions

On 7/27/2009 11:29:37 AM, ElSid wrote:
>Thank you. I am still having
>a hard time "seeing" and
>working with functions
______________________________

Using solvers does not come from clicking the fingers.
Attach your work sheet, Google this collab...

jmG
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