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6-Contributor

## Symbolic evaluation prime not working

Hello all,

Relatively new here and no experience using mathcad prime however I was looking for some guidance. I am working through a tutorial and trying to solve the following problem for lambda.

I am not sure where I am going wrong with using the solve (lambda) symbolic. From the looks of it possibly something to do with the pressures?

In the tutorial the solve symbolic yields the following:

Any help would be appreciated.

Callum

1 ACCEPTED SOLUTION

Accepted Solutions
23-Emerald III
(To:Callum1995)

Welcome to this community.

It's a good habit to attach your Prime worksheet along with your question. Most problems are easier understood and solved from using the worksheet, rather than looking at a mere picture (even if it paints a thousand words).

That is a third-order equation you are trying to solve. This means that there are three possible answers to the equation:

You did not state that you wanted a real answer (until you removed the units), so Prime tried to provide you all possibilities. But it introduces its own new variable _c and I bet it stole psi from one of your units, that is confusing.

You should realise that the symbolic processor in Prime normally doesn't 'know' units, at best it treats them like undefined variables.

There is a setting in Prime (under 'Calculation' => 'Calculation Options' ) where you can instruct it to observe units in symbolics. I guess that was used in the example you refer to.

My advice in general is that, if you want to work symbolically, then first do the symbolics and then fill in the numbers.

(The other two are much bigger expressions and contain complex numbers.)

This is the exact answer, and it's real (not complex). You see I've made lambda a function of the three arguments G, Pseal and so. You can call this function lambda with the (numerical) values of these three symbols to get a numeric answer.

But in case you just want a numeric answer, you can often better use the root function. In your case that might look like:

Success!

Luc

3 REPLIES 3
6-Contributor
(To:Callum1995)

Just as an update if I remove all units then it does work so why would the units interfere with the result?

23-Emerald III
(To:Callum1995)

Welcome to this community.

It's a good habit to attach your Prime worksheet along with your question. Most problems are easier understood and solved from using the worksheet, rather than looking at a mere picture (even if it paints a thousand words).

That is a third-order equation you are trying to solve. This means that there are three possible answers to the equation:

You did not state that you wanted a real answer (until you removed the units), so Prime tried to provide you all possibilities. But it introduces its own new variable _c and I bet it stole psi from one of your units, that is confusing.

You should realise that the symbolic processor in Prime normally doesn't 'know' units, at best it treats them like undefined variables.

There is a setting in Prime (under 'Calculation' => 'Calculation Options' ) where you can instruct it to observe units in symbolics. I guess that was used in the example you refer to.

My advice in general is that, if you want to work symbolically, then first do the symbolics and then fill in the numbers.

(The other two are much bigger expressions and contain complex numbers.)

This is the exact answer, and it's real (not complex). You see I've made lambda a function of the three arguments G, Pseal and so. You can call this function lambda with the (numerical) values of these three symbols to get a numeric answer.

But in case you just want a numeric answer, you can often better use the root function. In your case that might look like:

Success!

Luc

6-Contributor
(To:LucMeekes)

Good Evening,

Thanks for the useful information and insight on this one. I am still getting to grips with the various solve functions but that does indeed appear to have fixed the problem.

Best Regards,

Callum

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