C++ Home

by **Emilius** » Fri Feb 22, 2008 4:05 pm

Can you propose me some site, or something, where I can find some "shorter" way to work with matrices?

by **MXP** » Fri Feb 22, 2008 4:34 pm

I dont understand what you are looking for. What are you trying to do?

by **Emilius** » Sat Feb 23, 2008 2:39 am

I want to make a program that works with matrices - multiplication, determinant, etc. If I use the formulas, I learned in lectures, it shouldn't work for bigger matrices like 10000x10000 elements which are often used. I found a block matrix (I think that was the name), but I didn't found anything about their determinant (now I cannot find the site where I read about them

) That's all about.

by **DannyBoy** » Sat Feb 23, 2008 2:55 am

Do you specifically want to make a program or do you just need a program with which to manipulate matrices? If it's the latter, have a look at R.

by **Emilius** » Sat Feb 23, 2008 3:19 am

No, I don't need such a program - I want to make one

by **DannyBoy** » Sat Feb 23, 2008 3:24 am

Programming matrix algebra is quite common, especially as a homework assignment. Try typing "matrices" into the search facility and see! As for epic matrices, I'm not sure even MatLab could handle such calculations...

by **Alvaro** » Sat Feb 23, 2008 7:41 am

What exactly do you need? An algorithm for fast multiplication? Computing the determinant? What are your matrices like? Why do you need to do this (larger context)?

by **Emilius** » Sat Feb 23, 2008 10:43 am

I want to make a program that uses the finite elements method for structural analysis.

by **DannyBoy** » Sat Feb 23, 2008 10:59 am

Okay. That's certainly not a trivial program. Have you used C/C++ before?

I'm not overly familiar with FEM... So, do you have a set of equations in matrix form that then need to be solved using Gaussian elimination or some such thing?

by **Emilius** » Sat Feb 23, 2008 2:27 pm

I found an example - in wikipedia... but every matrix' determinant, for instance, may be calculated by using the common fromula - detA = sum(j=1..n) [(-1)^(i+j) * det(Aij * aij)], where A = [aij] i = 1..n and j = 1..n ... If I understood the question...

by **DannyBoy** » Sat Feb 23, 2008 2:36 pm

So, do you actually need any help then? :roll:

When posting questions it helps if you are concise, clear and specific. Suggested reading.

by **Emilius** » Sat Feb 23, 2008 2:40 pm

I made a mistake... it does not work... Block matrix cannot be used to calculate a determinant unless the partitioned matrices are nxn... I forgot it... :oops:

Whatever... I'll try to find some other way...

by **MXP** » Sat Feb 23, 2008 4:19 pm

If a matrix is not square then it already does not have a determinant. The method you got from Wikipedia will work just fine.

by **Emilius** » Sat Feb 23, 2008 4:46 pm

The common formula will be difficult to compute for a matrix 10000x10000, which is often used in FEM... If I try to use a block matrix, as I suggested earlier, and I have a matrix 505x505, for instance, I couldn't divide it by square matrices...

by **Emilius** » Sat Feb 23, 2008 5:03 pm

I think I just found a solution, but I must make sure that it works in any cases... I'll try it in the morning. Wish me luck

C++ Home

A matrix question...

A matrix question...

Who is online