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These units are not compatible

KL_13413435
3-Newcomer

These units are not compatible

Hi everyone,

I'm using Mathcad Prime Express 11 and I’ve run into a units-related error that I can't resolve.

At the end of my worksheet, I'm solving a system of equations using Find(...). When I try to evaluate the solution, Mathcad gives the following error: "These units are not compatible"

 I've attached: the full Mathcad worksheet

I'd really appreciate it if someone could help me identifywhich equation or variable is causing the unit conflict, and how I can fix it properly.

Thanks in advance!

KL_13413435_0-1747568368980.png

 

2 REPLIES 2
Werner_E
25-Diamond I
(To:KL_13413435)

I can't comment on the unit problem because I don't have Prime 11 installed and so can't open your sheet. That way I don't see which units you used for the results of your functions Pi2, F3, Pi3, Mi2, your vectors Gcxy, Gxy3 or your variables Iab, Is2 .

Are they all unit less, pure scalar values?. And are the vectors used or created by your functions simple n x 1 (presumable 2 x 1) vectors and not nested (= on vector inside another). Nested vectors sometimes are created unintentional by users because they are typing square brackets (= creating a matrix) instead of normal round parentheses.

If the variables are meant to have units (like meter or else) you have to add that unit for the guess values as well and to be on the safe side you might also write "0 m" instead of just "0".

 

What I noticed is your equation "R30y*h=0" where you demand that at least one the two variables involved must be zero (your guess for both is 1 !??). As "h" is nowhere else (in the visible part of the screenshot) used, why not set h=0 and don't use it in the solve block "find"?

 

 

Werner_E
25-Diamond I
(To:KL_13413435)

Just installed P11 and had a look in your sheet.

A lot of errors.

First one is the use of cspline for the definition of Omega1

.) apromega is not a function but rather a simple variable

.) cspline expects the values in the first vector (tj) to be in strict(!) ascendant order. They basically are, but the problem is that you have two equal values, two zeros, at the beginning:

Werner_E_0-1747582321176.png

So you either must get rid of one of the zeros (you would have  to get rid of one value in omega1j as well to make the vectors equal in length) or you replace the second zero by a very tiny, positive value as I did in the following screenshot.

Furthermore you will have to add the argument phi for ty when you call E1 as ty is a function, not a variable.

Its not necessary to add the unit in the definition of Omega1 - its gets its unit from the units in omega1j

And to make the plot you can't use Prime quickplot feature but must define a range for phi to be used for plotting. I have chosen the name phi.plot but you sure can simply use phi as the name for this range variable. Ia was not sure which range for phi you would like to see, but I guess the the range 0 to 45° pretty much shows all thats to be seen.

Werner_E_1-1747583077394.png

 

According the solve block - you can't add apples and oranges!

I just looked at your first equation you can't add quantities of different dimension like scalars, acceleration and force:

Werner_E_0-1747583670567.png

So you sure have to check all of your equations to make sure that you only add quantities of the same dimension.

Furthermore Gxy2 is NOT a 2 x 1 vector like the others but its a 1 x 2 row vector. Guess that was not done on purpose but to access a value in a row vector you need to provide both matrix indices:

Werner_E_1-1747583788465.png

Here is the reason why Gxy2 is a row vector and not a column vector:

Werner_E_0-1747591716496.png

 

 

 

 

 

 

 

 

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