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ptc-50909611-Visitor
1-Visitor
May 5, 2013
Question

Can someone help me?

  • May 5, 2013
  • 13 replies
  • 4203 views

Hi, I don't understand why it doen't calculate... Variables are okay, so why mathcad says that variables are undefined..Can someone help me?

13 replies

Werner_E
Werner_E25-Diamond I
25-Diamond I
May 5, 2013

You have used vector/matrix indices instead of literal indices.

The first are meant to access the elements of a vector or matrix. The latter are meant to name a variable as you intended and you get it by typing a period(.) instead of the opening square bracket ([).

Furthermore there is no comma (,) allowed in variable names, so I have changed them for underlines.

After I corrected those errors, variable A still was not recogniced - I don't know why. I retyped your A's and it worked. See attached.

BTW, there is no need to zip or rar the files you attach - it will be done automatically by this forum system.

ptc-50909611-VisitorAuthor
1-Visitor
May 5, 2013

Thanx. A was also matrix, not variable One more question: why I can't add something new to the formula, it doesn't type multiplication...

Werner_E
Werner_E25-Diamond I
25-Diamond I
May 5, 2013

Jonas Jonaitis wrote:

Thanx. A was also matrix, not variable One more question: why I can't add something new to the formula, it doesn't type multiplication...

I can't tell as I don't see what exactly you are trying to do, but you sure can edit your expression and add multiplication or whatever.

Editing expressions in Mathcad can be a little tricky sometimes, to say the least.

You will have to acquaint yourself with the editing features, especially the space and insert keys and their effect on the blue editing cursor..

Mathcad 15 (and lower) has some really good help facilities. For help on expression entering and editing you may go to help/tutorials/Getting started Primers.

ptc-50909611-VisitorAuthor
1-Visitor
May 5, 2013

I get numbers. But I need literal expression.

Werner_E
Werner_E25-Diamond I
25-Diamond I
May 5, 2013

Jonas Jonaitis wrote:

I get numbers. But I need literal expression.

Even symbolic evaluation (-->) will consider and respect the values of variables.

You had assigned values to all of your variables, so these values are automatically inserted and evaluated.

You have four choices:

1) define the function f and evaluate the derivatives before you define the values for A, E, etc.

2) delete the values, you can still evaluate f by typing f(0.00125, 210*10^9,.....)=

3) use different variable names when you symbolically evaluate your derivatives

4) "clear" the variables for symbolic evaluation by typing A:=A, E:=E etc. The variables will still have their value for numeric evaluation but not for symbolic eval.

You may try to combine the symbolic eval with simplify or factor to make the result more handsome. Mathcads abilities concernnig symbolic evaluations and simplifications are not top notch, so don't expect too much.

BTW, I am still confused by your variables A and E. They are not normal variables but they are no matrices, as you wrote. They look like normal variables, but when I type E= I'm getting the error that the variable is unknown. How did you insert those variable names and what version of Mathcad are you using?

ptc-50909611-VisitorAuthor
1-Visitor
May 5, 2013

Which command do you use for evaluation symbolically? Expressions aren't beautiful. How to reduce number places after comma? I use Mathcad v15.evaluation.png

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