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Topic: Problem solving nonlinear equations with matrices
Replies: 4   Last Post: Dec 3, 2012 2:58 PM

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 Joshua Posts: 3 Registered: 12/1/12
Re: Problem solving nonlinear equations with matrices
Posted: Dec 3, 2012 2:58 PM

"Joshua " <Hogy88@aol.com> wrote in message <k9dh9o\$mn6\$1@newscl01ah.mathworks.com>...
> Hello,
>
> I am working with the Finite Element Method using MATLAB and I have run into a technical problem. For the basic finite element procedure, a stiffness matrix K and a force vector F are created, and the results we want to find are solved using
>
> d=K\F
>
> where K and F have no variables, only numbers. Now, however, I am doing a vibration problem and need some help to put a nonlinear equation into the matrix, or to solve it simultaneously.
>
> Here's my problem:
>
> I have a square matrix K of only numbers and my force vector F is zeros. I cannot just solve
>
> d=K\F
>
> because it gives me the trivial zero solution. I have to insert an equation based on a diagonal matrix M such that
>
> M_i*d(i)^2=1 (sum on i from 1 to the size of the K matrix)
>
> or M11*d1^2 + M22*d2^2 + ... + Mnn*dn^2 = 1
>
> where n is the number of rows/columns in K.
>
> My procedure is to remove one equation (or row) from the K matrix, leaving n-1 equations, and to solve these equations with the M_i*d(i)^2=1 equation to give me a nonzero d solution. My problem is...how? I am new to MATLAB and have no clue how to do this. I've tried using fsolve but keep getting various error messages.
>
> Help?!

Thanks, that worked out pretty well.

Date Subject Author
12/1/12 Joshua
12/1/12 Nasser Abbasi
12/2/12 Joshua
12/2/12 Steven Lord
12/3/12 Joshua