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chapters/matrix_methods/gaussian_elimination/gaussian_elimination.md

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# Gaussian Elimination
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So, how exactly do we go about solving a system of linear equations? Well, one way is _Gaussian Elimination_, which you may have encountered before in a math class or two. The basic idea is that we take a system of equations,
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How exactly do we go about solving a system of linear equations? Well, one way is _Gaussian Elimination_, which you may have encountered before in a math class or two. The basic idea is that we take a system of equations,
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## The Method
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Here I should point out that Gaussian elimination makes sense from a purely analytical point of view. That is to say that for small systems of equations, it's relatively straightforward to do this method by hand; however, for large systems, this \(of course\) become tedious and we will need to find an appropriate numerical solution. For this reason, I have split this section into two parts. One will cover the analytical framework, and the other will cover an algorithm you can write in your favorite programming language.
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Here I should point out that Gaussian elimination makes sense from a purely analytical point of view. For small systems of equations, it's relatively straightforward to do this method by hand; however, for large systems, this \(of course\) become tedious and we will need to find an appropriate numerical solution. For this reason, I have split this section into two parts. One will cover the analytical framework, and the other will cover an algorithm you can write in your favorite programming language.
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In the end, reducing large systems of equations boils down to a game you play on a seemingly random matrix where you have the following moves available:
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If that value is $$0$$, the matrix is singular and the system has no solutions. Feel free to exit here, but I'm powering through by moving on to the next column, baby!
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2. Swap the row with the highest valued element with the current row.
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[import:4-33, lang:"haskell"](code/haskell/gaussianElimination.hs)
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{% endmethod %}
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As with all code, it takes time to fully absorb what is going on and why everything is happening; however, I have tried to comment the above code with the necessary steps. Let me know if anything is unclear!
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Now, to be clear: this algorithm creates an upper-triangular matrix. In other words, it only creates a matrix in *Row Echelon Form*, not * **Reduced** Row Echelon Form*! So what do we do from here? Well, we continue further reducing the matrix, but with a twist: using the *Back-Substitution*.
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The back-substitution method is precisely what we said above, but for every pivot starting from the bottom right one.

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