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MATHCAD: the symbolic result returned is too large to be displayed

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ziops

ziops

Civil/Environmental
Aug 13, 2010
7
Problem with Mathcad: I have a symbolic matrix 9x9, and its determinant should be the argument of another function of only 1 variable like- f(x). Unfortunately when I evaluate symbolically the matrix, Mathcad returns the text: "the symbolic result returned is too large to be displayed but it can be assigned to a function or variable". That's what i want, but how to do it?
How do I assign it to a function?
Just do a normal assign, eg f(x):= |M| (or |M(x)|, doesn't work!
Please help!!! I'm getting crazy!! It's growing like a quiet private matter.
Thank you very much
 
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I guess the more germane question is why you even need a symbolic solution? Isn't the end goal to numerically evaluate the determinant? If so, then why wouldn't you use the numerical determinant functions?

TTFN

FAQ731-376
 
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No IRstuff, I'm sorry I wasn't exhausted. I can't evaluate it numerically! In the matrix there are about 30 complex three times nested functions of a single variable (x) and I need a symbolic solution of |M(x)|. If I obtain it I can write the equation |M(x)|=0 so then I can find those values of the variable x who satisfy that condition, that is my end goal, my purpose. Otherwise how could I do if I don't evaluate the determinant numerically?

Thank you (I apologize for my awful English)
 
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|M(x)|=0 does not necessarily require a symbolic solution. You can use a Solve Block to numerically find the value of x that sets the determinant to zero, or at least, nearly zero.

Something like:

x:5 (guess value)

Given (start solve block)

|M(x)|=0

x:find(x) (end solve block and assign result back to x)

TTFN

FAQ731-376
 
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I already tried it. I wrote:
x:=20
Given
|M(x)|=0 (boolean equal ctrl+)
Find(x)=
Unfortunately when I write Find(x) it bencomes red and Mathcad says: "This variable is undefined"!! (I think it refers to x).
But it is obviously undefined!! It's symbolic, it's a variable, it can't be numerically defined!Is it wrong?
 
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Seeing the sheet would be more useful

TTFN

FAQ731-376
 
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Well, have you tried to graph your function? It doesn't seem to produce much in the way of anything that would result in 0

TTFN

FAQ731-376
 
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I've just tried to graph it. MC says "All evaluations resulted in either an error or a complex result". I don't know what does it mean exactly, but I'm sure that matrix and the nested functions too are correct, so there must be a a solution (it represents the crictical load for a three floors frame).
In the following file there is an easier similar problem resolved (the matrix is 3x3) and the function is graphed too: both problems are solvable, I'm sure.
 
 http://files.engineering.com/getfile.aspx?folder=cd0ed4d6-0630-42f7-8883-bfb134cef7bf&file=Determinante_3x3.xmcd
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Well, you can just pick arbitrary values of x and evaluate the determinant. If you can't get the determinant to switch sign, then there is no solution to your problem.

TTFN

FAQ731-376
 
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At last I was able to find the result picking many arbitrary values in growing order. It was difficult because the function is almost vertical in that point, so that the determinant switches sign in a teeny gap. Tha value is included in the gap x=927.65 and x=927.66 (KN/m). That's not the value I was waiting for but now the problem has a solution! Perhaps I mad a mistake when defining the functions. However I'm really grateful to you for your help.
Thank you IRstuff, thank you!
 
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