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Need help with matrices!by SamMcCrae
Tags: matrices 
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#1
Nov1512, 10:52 AM

P: 8

How can I turn a 5x5 matrix into a 4x4? I really cannot remember and I need to do it in a coursework I am doing :/ I have a handout on how to do 4x4 into 3x3 but the handout is very confusing.



#2
Nov1512, 12:08 PM

P: 5,462




#3
Nov1512, 01:56 PM

P: 8




#4
Nov1512, 03:09 PM

Mentor
P: 18,022

Need help with matrices!
Do you mean that you're given a 5x5matrix and a 4x4matrix and you want to find out whether they have the same determinant?? Is that what you want to solve?



#5
Nov1512, 03:55 PM

P: 8




#6
Nov1512, 03:58 PM

Mentor
P: 18,022

How can a 5x5matrix be the same as a 4x4matrix?? They are not the same by definition. Can you give an example of what exactly you mean?? 


#7
Nov1512, 04:03 PM

P: 8




#8
Nov1512, 04:28 PM

P: 772




#9
Nov1512, 04:39 PM

P: 8




#10
Nov1612, 02:46 PM

P: 8

Bumpidy bump



#11
Nov1612, 02:59 PM

P: 5,462

Well sam, I see you are talking about partitioning the stiffness matrix when you have a matrix equation relating the vector of forces (loads) to the vector of deflections.
You can do this because you are introducing a compatibility relationship. Partitioning is not the same as reducing the matrix. Why did you not post this as an engineering question where it might have been more quickly recognised? What is the actual problem you are trying to solve?  please name your symbols. Does this help? http://algebra.math.ust.hk/matrix_li.../lecture.shtml 


#12
Nov1612, 03:05 PM

Mentor
P: 18,022

I'll move it back to engineering... 


#13
Nov1612, 03:06 PM

P: 5,462

Oh sorry.



#14
Nov1612, 03:59 PM

P: 5,462

You are able to reduce the size of the matrix because the values of some deflections are known, eg usually zero at supports.
Thus a set of 5 equations can be reduced to four if one deflection is zero. This is what was meant by insert the zero in your notes. I cannot say more without more detail. 


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