3 Replies Latest reply: Dec 30, 2011 11:15 AM by lvl107

# LU Decomposition Method, Really Need Help ASAP

Really need help with these 2 problems:

Find the solution to Problems using the LU Decomposition method:

1.

X1 + X2 = 3

4X1 - 2X2 = 2

2. Find the set of equations for:

X1 + 2X2 - X3 = 3.1

-3X1 + X2 +X3 = 1.4

-X1 - X2 + 4X3 = 7.3

Thanks Guys!

• ###### Re: LU Decomposition Method, Really Need Help ASAP

Simply create you matrix M and apply the lu(M) function.

The manual gives details of the augmented matrix it returns, that is, it has the permutation P, L and U matrixes side by side in one big rectangular matrix.

The permutation matrix simply converts the original matrix M into an easier to solve (by the computer) matrix, for which the L and U are then provided.

In general, Mathcad is implicit (just use lu() ), rather than explicit (we don't write matlab code!)

It is possible to write a long(ish) programme function to do the pseudo code that may have been given in class, but usually we don't bother, given we have the function already ;-)

Philip

• ###### Re: LU Decomposition Method, Really Need Help ASAP

Maybe this is only a similar one.