4 x 4 or 5 x 4 Matrix
03-05-2015, 03:14 AM
Post: #1
 marcusnicolas1 Junior Member Posts: 39 Joined: Dec 2014
4 x 4 or 5 x 4 Matrix
Is there a way to solve a system of linear equations with 4 or 5 variables? aka 4 x 4 or 5 x 5 matrix. Can someone please help me with this problem. Thank you
03-05-2015, 03:33 AM
Post: #2
 Helge Gabert Senior Member Posts: 467 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
Have a look at LSQ, with your coefficients in a square matrix (4x4 or 5x5), and your right hand side values in a column matrix (4x1 or 5x1).
03-05-2015, 04:28 AM
Post: #3
 Han Senior Member Posts: 1,883 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
Define your matrix $$A$$ and your vector $$b$$. Then simply type $$b / A$$ in the calculator. You should check to see whether the matrix has determinant 0 (inconsistent) to avoid erroneous results.

Graph 3D | QPI | SolveSys
03-05-2015, 06:25 AM
Post: #4
 cyrille de brébisson Senior Member Posts: 1,047 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
hello,

look at the RREF function, it might give you the answer that you are looking for.

cyrille
03-06-2015, 01:28 AM
Post: #5
 marcusnicolas1 Junior Member Posts: 39 Joined: Dec 2014
RE: 4 x 4 or 5 x 4 Matrix
So how do I put this into the calculator. I see the RREF but when I try to use it, all it get is RREF() I do not see how to put things into matrix form. Can anyone help me with this please
03-06-2015, 01:46 AM
Post: #6
 Helge Gabert Senior Member Posts: 467 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
If you would like to use LSQ, here you go:

LSQ([[c11 c12 . . c15][c21 . . c25] . . . [c51 . . c55]],[[b1 . . b5]])

c's are the coefficients of your linear system. b's are the r.h.s. values.

Also look at the built-in help for LSQ - - there is a 2x2 example.
03-06-2015, 01:50 AM
Post: #7
 Han Senior Member Posts: 1,883 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
(03-06-2015 01:28 AM)marcusnicolas1 Wrote:  So how do I put this into the calculator. I see the RREF but when I try to use it, all it get is RREF() I do not see how to put things into matrix form. Can anyone help me with this please

1. Go to the matrix editor: [Shift] [4]
2. Select a matrix to edit and press (for example, choose M1): [Enter]
3. Enter the values into the matrix (let's assume we're entering our coefficient matrix); exit by pressing: [Esc]
4. Edit a new matrix: [Shift] [4] and select another matrix (for example M2)
5. Enter the constants column into this matrix. For example, if your system is
$\begin{array}{ll} 2x+3y & = 5\\ 5x+2y & = 1 \end{array}$
then the you would enter the 5 and 1 (as a column) into M2
6. In the Home screen, just type: M2 / M1

Or, you can enter in the entire system into a single matrix (again, let's pretend we're using M1) and just type RREF(M1) at the home screen.

Graph 3D | QPI | SolveSys
03-06-2015, 08:59 PM
Post: #8
 John Colvin Member Posts: 173 Joined: Dec 2013
RE: 4 x 4 or 5 x 4 Matrix
(03-06-2015 01:28 AM)marcusnicolas1 Wrote:  So how do I put this into the calculator. I see the RREF but when I try to use it, all it get is RREF() I do not see how to put things into matrix form. Can anyone help me with this please

You can also use RREF with the coefficient matrix directly without the need of first storing the matrix by entering RREF([]) in CAS mode, where [] is your matrix entered directly using the matrix template.
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