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Lilli1-Visitor
1-Visitor
February 14, 2012
Solved

ARGH! Where is my mistake

  • February 14, 2012
  • 14 replies
  • 7409 views

Dear everybody!

You find enclosed my MathCAD file.

My equations depend of THETA, I know by mesure the pressure following THETA.

Why FI"(THETA) isn't a function?

Best answer by Fred_Kohlhepp

Actually, if you import both columns your sheet will work as written.

One of the things Mathcad can do isfit functions to data. Before I realized that importingg the whole file solved your problem, I was trying to develop P as a function of theta. That would allow you to use functions instead of vectors.

14 replies

wayne12-Amethyst
12-Amethyst
February 14, 2012

Are the values of Theta in the excell table in degrees?
If so then assign the degree unit to theta ( theta:=theta*deg) and drop the degree assignments in the functions.

Mathcad will convert to radians internally, and do computations in radians.

It's a little confusing using angular velocity in radians/s and funcitons that have theta in degrees combined with functions with theta in radians.

Fred_Kohlhepp23-Emerald I
23-Emerald I
February 14, 2012

The sheet you posted has no data for theta or P(theta); the readfile structuresdon't store the data. As soon as I create values for theta, all the functions develop values.

Lilli1-VisitorAuthor
1-Visitor
February 15, 2012

Thanks all! Unfortunately, the functions don't all develop! If you look your sheet, j"(q) and after doesn't develop, Strangely if I write

j"(q):=(j'(q)*j'(q)-q'²)*tanj(q) it's develop, why. It's the same thing after ??????

wayne12-Amethyst
12-Amethyst
February 15, 2012

You need to vectorize some of the equations.

Mathcad will automatically vectroize, sometimes. I've see situations where Mathcad appeared to vectorize automatically, because it gave multiple results. But if you then vectorize, the answer is different (and correct).

Some of you equations that don't produce multiple results just need to be vectorized, but others should be checked to see if the result when vectorized is the same.

You could also put Theta=0..rows()Theta and P=0..rows(P) at the beginning and it will do the same thing (I did not try though).

It also looks like you need to assign units to P, P=P*psi, or whatever.

Lilli1-VisitorAuthor
1-Visitor
February 15, 2012

Hello Wayne,

I'm not sure to understand. I added the unit for the P value after your fist respond. I come to solved the problem, I suppresed the excel relation for Theta but now I don't know how to use my pressure.

Lilli1-VisitorAuthor
1-Visitor
February 16, 2012

Thanks at all ! Currently, I continue to improve my systeme. I think that is not finish but for the moment the problem are solve.

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