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JohnMiddleton1-Visitor
1-Visitor
August 4, 2011
Solved

Multiple variable feeds

  • August 4, 2011
  • 2 replies
  • 4466 views

Hi,

We have a formula that requires two range variables feeding from the first equation into the second equation. The variables are dependent on each other i.e should R.as = 0.097 then a.s = 0.8 - please see attached example. The problem is that we do not know how to solve within mathcad.

Any help would be most appreciated.

John M.

Best answer by MikeArmstrong

Like the attached?

Mike

2 replies

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
August 4, 2011

You defined functions Rt(as) and Rtm(as). These will evaluate for any value you want to put innto the parentheses: Rt(0.8m) = 0.097 m ohm.

You can't make a vector from a range function, so Ras doesn't work.

But you can plot your two functions against the range variable as; Rt is a straight line, and Rtm looks like a parabola.

See attached!

Good Luck!

J
JohnMiddleton1-VisitorAuthor
1-Visitor
August 4, 2011

Thanks for your help Fred. I think that will solve it. I'll have a study and come back to you.

John

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
August 4, 2011

WOW!!

That's an impressive sheet.

Before it opened I had to assume that you weren't scheming to trash my computer with a malevolent scripted component. (Good thing you're a reputable PTC Hero!)

Then I found myself looking at a function that I didn't recognise (vec()) even though I've used Mathcad for longer than I like to admit. Fortunately I too have downloaded RIchard's and Phillip's utility sheets so when I recognised and expanded the collapsed area at the top of the page I could solve the mystery.

But here's my gripe (bear with an old man):

The people who asked for help are obviously new to Mathcad, just looking at the sheet we old pros can tell. So why have you added such complexity to their problem? It doesn't help them understand how to use Mathcad to attack the problem. When they type vec(0.1,0.2...10) into a raw sheet (without the utility area) how are they going to understand why it doesn't work; I don't think they really have grasped the differences between functions, vector, and range variables fully yet. Okay, you created vectors for them. They could web surf over to John Doyle and use EXCEL if they wanted vectors.

When we're helping newbies, use the loving maxim: KISS (Keep It Simple, Sir.

M
MikeArmstrong1-Visitor
1-Visitor
August 4, 2011

Slightly different approach to Fred. Am I missing something?

Mike

J
JohnMiddleton1-VisitorAuthor
1-Visitor
August 5, 2011

Hi,

I think both of the answers are not right.

What we are trying to do with the final equation (Rtm=..) is work out the new resistance of our subject matter based on the previous resistance found from RT(as) and based on the distance (as).

The answers to RT(as) obviously provide a range of answers in relation to (as). What we require to do is tell MC to input both variables into the final equation to give us another range of answers (should be 20 answers each time).

See tables in original MC. The answers are related in that RT(as) is beholden by (as) so that as an example if (as) is equal to 0.8 then RT(as) is 0.097, if (as) is 0.81 then RT(as) is 0.099..... if (as) is 1.0 then RT(as) is 0.121

Having manualy worked out the first, tenth and last answer (as a check) we know the following to be true:

Rtm = 0.13 when RT(as) is 0.097 and (as) is 0.8

Rtm = 0.161 when RT(as) is 0.108 and (as) is 0.89

Rtm = 0.202 when RT(as) is 0.121 and (as) is 1.0

We have renamed RT(as) as Ras for purposes of a further equation. This should not affect the answer as Ras simply becoms the range Rt(as).

I hope this helps to clarify what we are trying to do.

Thanks,

John

M
MikeArmstrong1-VisitorAnswer
1-Visitor
August 5, 2011

Like the attached?

Mike

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