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Simultaneous Linear Equations Gaussian Elimination with Partial Pivoting
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Naïve Gauss Elimination Pitfalls
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Pitfall#1. Division by zero
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Is division by zero an issue here?
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Is division by zero an issue here? YES
Division by zero is a possibility at any step of forward elimination
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Pitfall#2. Large Round-off Errors
Exact Solution
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Solve it on a computer using 6 significant digits with chopping
Pitfall#2. Large Round-off Errors Solve it on a computer using 6 significant digits with chopping
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Pitfall#2. Large Round-off Errors
Solve it on a computer using 5 significant digits with chopping Is there a way to reduce the round off error?
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Increase the number of significant digits
Avoiding Pitfalls Increase the number of significant digits Decreases round-off error Does not avoid division by zero
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Gaussian Elimination with Partial Pivoting
Avoiding Pitfalls Gaussian Elimination with Partial Pivoting Avoids division by zero Reduces round off error
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Gauss Elimination with Partial Pivoting http://nm.MathForCollege.com
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What is Different About Partial Pivoting?
At the beginning of the kth step of forward elimination, find the maximum of If the maximum of the values is in the p th row, then switch rows p and k.
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Which two rows would you switch?
Example (2nd step of FE) Which two rows would you switch?
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Example (2nd step of FE) Switched Rows
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Gaussian Elimination with Partial Pivoting
A method to solve simultaneous linear equations of the form [A][X]=[C] Two steps 1. Forward Elimination 2. Back Substitution
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Gauss Elimination with Partial Pivoting Example
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Example 2 Solve the following set of equations by Gaussian elimination with partial pivoting 17
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Example 2 Cont. Forward Elimination Back Substitution 18
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Forward Elimination 19
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Number of Steps of Forward Elimination
Number of steps of forward elimination is (n-1)=(3-1)=2
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Forward Elimination: Step 1
Examine absolute values of first column, first row and below. Largest absolute value is 144 and exists in row 3. Switch row 1 and row 3.
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Forward Elimination: Step 2
Examine absolute values of second column, second row and below. Largest absolute value is and exists in row 3. Switch row 2 and row 3.
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Back Substitution 23
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Gaussian Elimination with Partial Pivoting Solution
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THE END
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