GAUSS-ELEMINATION METHOD
GAUSS ELEMINATION METHOD :
 The method is based on the idea of reducing the given system of equations
Ax = B; to an upper triangular system of equations Ux = z, using
elementary row operations .That is, the solutions of both the systems are
identical. Here 𝑥 = 𝑢𝑛𝑘𝑛𝑜𝑤𝑛 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒′ 𝑠 𝑚𝑎𝑡𝑟𝑖𝑥
 We illustrate the method using the 3 × 3 system
 𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1 ∶ R1
 𝑎21 𝑥 + 𝑎22 𝑦 + 𝑎23 𝑧 = 𝑏2 ∶ 𝑅2
 𝑎31 𝑥 + 𝑎32 𝑦 + 𝑎33 𝑧 = 𝑏3 ∶ 𝑅3
 Now to make the patter of equation upper triangular matrix we have to
use the operation :
 𝑅𝑖 = 𝑅𝑖 −
𝑎 𝑖𝑘
𝑎 𝑘𝑘
∗ 𝑅 𝑘
 Where i=(k+1),(k+2),……n ; k= coloumn number
 So after applying the operation the equation becomes :
 𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1
 0+𝑎′12 𝑦 + 𝑎′13 𝑧 = 𝑏′2 [𝑅′2 = 𝑅2 −
𝑎21
𝑎11
∗ 𝑅1 ]
 0+𝑎′12 𝑦 + 𝑎′13 𝑧 = 𝑏′3 [ 𝑅′3 = 𝑅3 −
𝑎31
𝑎11
∗ 𝑅1 ]
 then after that we have to apply the same process to make
that pattern to a upper triangular matrix.
 𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1
 0+𝑎′22 𝑦 + 𝑎′23 𝑧 = 𝑏′2
0 + 0 + 𝑎′′33 𝑧 = 𝑏′′3 [ 𝑅′′3 = 𝑅′3 −
𝑎32
𝑎22
∗ 𝑅2 ]
 the successively we can find the values Z, Y, X.
 For example we take three equations:
𝑥 − 2𝑦 + 9𝑧 = 8
3𝑥 + 𝑦 − 𝑧 = 3
2x − 8𝑦 + 𝑧 = −5
 Now we have to make it a upper triangular matrix using the
operation:
 𝑅2 = 𝑅2 −
𝑎21
𝑎11
∗ 𝑅1 𝑅2 = 𝑅2 − 3/1 ∗ 𝑅2
 They become : 𝑥 − 2𝑦 + 9𝑧 = 8
 0 + 7𝑦 − 28𝑧 = −21
 0 − 4𝑦 − 17𝑧 = −21
 To get the pattern of upper triangular matrix we again do the
operation:
The operation is : 𝑅3 = 𝑅3 − −4/7 ∗ 𝑅2
Now they become : : 𝑥 − 2𝑦 + 9𝑧 = 8
0 + 7𝑦 − 28𝑧 = −21
0 + 0 − 33𝑧 = −33
So that : 𝑧 = 1;
𝑦 =
−21+28𝑧
7
= 1;
𝑥 = 8 − 9𝑧 + 2𝑦 = 1 .
The set of solution is : X=1; Y=1; Z=1.
THANK YOU

GAUSS ELIMINATION METHOD

  • 1.
  • 2.
    GAUSS ELEMINATION METHOD:  The method is based on the idea of reducing the given system of equations Ax = B; to an upper triangular system of equations Ux = z, using elementary row operations .That is, the solutions of both the systems are identical. Here 𝑥 = 𝑢𝑛𝑘𝑛𝑜𝑤𝑛 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒′ 𝑠 𝑚𝑎𝑡𝑟𝑖𝑥  We illustrate the method using the 3 × 3 system  𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1 ∶ R1  𝑎21 𝑥 + 𝑎22 𝑦 + 𝑎23 𝑧 = 𝑏2 ∶ 𝑅2  𝑎31 𝑥 + 𝑎32 𝑦 + 𝑎33 𝑧 = 𝑏3 ∶ 𝑅3  Now to make the patter of equation upper triangular matrix we have to use the operation :  𝑅𝑖 = 𝑅𝑖 − 𝑎 𝑖𝑘 𝑎 𝑘𝑘 ∗ 𝑅 𝑘  Where i=(k+1),(k+2),……n ; k= coloumn number
  • 3.
     So afterapplying the operation the equation becomes :  𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1  0+𝑎′12 𝑦 + 𝑎′13 𝑧 = 𝑏′2 [𝑅′2 = 𝑅2 − 𝑎21 𝑎11 ∗ 𝑅1 ]  0+𝑎′12 𝑦 + 𝑎′13 𝑧 = 𝑏′3 [ 𝑅′3 = 𝑅3 − 𝑎31 𝑎11 ∗ 𝑅1 ]  then after that we have to apply the same process to make that pattern to a upper triangular matrix.  𝑎11 𝑥 + 𝑎12 𝑦 + 𝑎13 𝑧 = 𝑏1  0+𝑎′22 𝑦 + 𝑎′23 𝑧 = 𝑏′2 0 + 0 + 𝑎′′33 𝑧 = 𝑏′′3 [ 𝑅′′3 = 𝑅′3 − 𝑎32 𝑎22 ∗ 𝑅2 ]  the successively we can find the values Z, Y, X.
  • 4.
     For examplewe take three equations: 𝑥 − 2𝑦 + 9𝑧 = 8 3𝑥 + 𝑦 − 𝑧 = 3 2x − 8𝑦 + 𝑧 = −5  Now we have to make it a upper triangular matrix using the operation:  𝑅2 = 𝑅2 − 𝑎21 𝑎11 ∗ 𝑅1 𝑅2 = 𝑅2 − 3/1 ∗ 𝑅2  They become : 𝑥 − 2𝑦 + 9𝑧 = 8  0 + 7𝑦 − 28𝑧 = −21  0 − 4𝑦 − 17𝑧 = −21  To get the pattern of upper triangular matrix we again do the operation:
  • 5.
    The operation is: 𝑅3 = 𝑅3 − −4/7 ∗ 𝑅2 Now they become : : 𝑥 − 2𝑦 + 9𝑧 = 8 0 + 7𝑦 − 28𝑧 = −21 0 + 0 − 33𝑧 = −33 So that : 𝑧 = 1; 𝑦 = −21+28𝑧 7 = 1; 𝑥 = 8 − 9𝑧 + 2𝑦 = 1 . The set of solution is : X=1; Y=1; Z=1.
  • 6.