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10-29-2015
06:37 AM

10-29-2015
06:37 AM

Mixed units in matrices

I am trying to set up the equations for the solution of a matrix displacement problem in structural analysis, i.e., F=KU, where F = force matrix {4X1}, K=stiffness matrix {4X4}, and U=displacement matrix {4X1}. However, Mathcad will not accept the definition of these matrices with mixed units. Do I have to define these matrices as unitless and track the results by hand?

Thank you for your assistance.

9 REPLIES 9

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10-29-2015
10:17 AM

10-29-2015
10:17 AM

Re: Mixed units in matrices

Mathcad 15 does not permit mixed units in matrices. Mathcad Prime does (it's one of the few things where Prime is better).

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10-29-2015
10:21 AM

10-29-2015
10:21 AM

Re: Mixed units in matrices

Richard Jackson wrote:

Mathcad Prime does (it's one of the few things where Prime is better).

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10-29-2015
10:17 AM

10-29-2015
10:17 AM

Re: Mixed units in matrices

Thats a drawback in older Mathcad versions and one of the very few benefits of Prime.

in Prime you can have different dimensions in a matrix, but in MC15 and below you unfortunately can't.

WE

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10-29-2015
10:20 AM

10-29-2015
10:20 AM

Re: Mixed units in matrices

Am I right in thinking that an older version of Mathcad accepted mixed unit arrays?

Mike

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10-29-2015
11:09 AM

10-29-2015
11:09 AM

Re: Mixed units in matrices

No, it's not been possible in any version prior to Prime.

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10-29-2015
11:15 AM

10-29-2015
11:15 AM

Re: Mixed units in matrices

Maybe the constant feature requests over the years clouded my thoughts.

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10-29-2015
11:27 AM

10-29-2015
11:27 AM

Re: Mixed units in matrices

Maybe 15-20 years from now we will be having the same discussion about multi-dimension arrays (with or without mixed units)

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10-29-2015
10:27 AM

10-29-2015
10:27 AM

Re: Mixed units in matrices

I agree with Richard & Werner. However, it might still be possible to achieve your overall goal without switching to Prime or omitting units. Would you be able to achieve what you want by simply splitting your calculations into two portions: one for load/displacement, and the other for moment/rotation?

Finally, I would encourage you to include your units in the definition of the variables rather than in the equations. For example:

Use:

Y1 := 1*kip

F12 := Y1...

Instead of:

Y1 := 1

F12 := Y1*kip...

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10-29-2015
03:33 PM

10-29-2015
03:33 PM

Re: Mixed units in matrices

But only in Mathcad PM (Prime Minister)

we can do so - change units of separate elements in outputted array: