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Symbolics Help

ELSID
4-Participant

Symbolics Help

Working with symbolics is not my strong point. Need a little help with questions on the sheet. Based off of Dr. Alan Stevens critical thickness insulation work. Mostly symantics ... so driving me crazy.

1 ACCEPTED SOLUTION

Accepted Solutions

ElSid wrote:

Did not understand the second part

AlanStevens wrote:

--> Replace T.sat with either T.s or just Tsat (i.e. no subscript) It will then result in T.s - T.air rather than -(T.air - T.sat ) .

See attached.

Alan

View solution in original post

11 REPLIES 11
RichardJ
19-Tanzanite
(To:ELSID)

One thing you should always remember when using the symbolic processor is that it does not make implicit assumptions like you do. If it doesn't do what you expect then a liberal dose of the "assume" keyword can work wonders

ELSID
4-Participant
(To:RichardJ)

Arrg! I had the R and t>0 on a previous section ... thanks for the catch. Is there a way of forcing the 2pi to the numerator? What about the negative sign?

RichardJ
19-Tanzanite
(To:ELSID)

Solve first, then simplify to get rid of the weird formatting, then force the ln formatting.

ElSid wrote:

Is there a way of forcing the 2pi to the numerator?

Think of P/2pi as P1 and solve for P1. Then set P:=P1*2pi ->

What about the negative sign?

Replace T.sat with either T.s or just Tsat (i.e. no subscript) It will then result in T.s - T.air rather than -(T.air - T.sat ) .

Alan

RichardJ
19-Tanzanite
(To:AlanStevens)

Replace T.sat with either T.s or just Tsat (i.e. no subscript) It will then result in T.s - T.air rather than -(T.air - T.sat ) .

Interesting observation. I wonder why that makes any difference. I would expect the formatting to be independent of the choice of variable name.

ELSID
4-Participant
(To:AlanStevens)

Did not understand the second part

AlanStevens wrote:

--> Replace T.sat with either T.s or just Tsat (i.e. no subscript) It will then result in T.s - T.air rather than -(T.air - T.sat ) .

ElSid wrote:

Did not understand the second part

AlanStevens wrote:

--> Replace T.sat with either T.s or just Tsat (i.e. no subscript) It will then result in T.s - T.air rather than -(T.air - T.sat ) .

See attached.

Alan

ELSID
4-Participant
(To:ELSID)

Revisitng a post with a file that I had working in MathCAD 14 and for some reason will not work in MathCAD 15 M030. Hoping the Collab can help. Problem starts with equation 5 where it appears I can not longer define a variable based on a symbolic. See screenshot

Capture.JPG

Werner_E
24-Ruby V
(To:ELSID)

Thats "normal" (nevertheless strange) behaviour that you dont see a symbolic result when you use a symbolic inline evaluation in an assignment.

Simply evaluate P.F later and you will see the correct result.

1.png

You used a font which seems not to be installed on my machine, so the nominator is shown as a small rectangle.

Depending on how wide you'd like your sheet to be spread you might consider changing that.

ELSID
4-Participant
(To:Werner_E)

Werner,

MathCAD just crashed. Why did it work in MathCAD 14? You are correct and I will revise the sheet. I shouldn't have to to do this much re-work btween 14 and 15!

Werner_E
24-Ruby V
(To:ELSID)

ELSID wrote:

Werner,

MathCAD just crashed. Why did it work in MathCAD 14? You are correct and I will revise the sheet. I shouldn't have to to do this much re-work btween 14 and 15!

I am using MC15 (M030) and didn't experience that kind of problem.

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