"Gaussian Elimination" Implementation in C++ #555

rishvic · 2018-12-17T14:08:23Z

Added an implementation for the Gaussian Elimination algorithm in C++, and encapsulating it in a C++ class so as to make it user-friendly, and used some of recent C++ features such as multi-dimensional vector to create matrix. Any advice for changes or such is appreciated.

rishvic · 2018-12-18T13:45:02Z

In my second commit, I just changed it so as to make sure that the row with highest absolute pivot moves up.

leios · 2018-12-23T23:41:08Z

Unfortunately, we have a PR for gaussian elimination in C++ (#258). I'll see what the status is on that PR and get back to you. Sorry it's taking so long.

Gathros · 2019-01-04T11:46:25Z

The other pull request is closed, so this is the main one for Gaussian elimination.

Gathros

I didn't review the algorithm, I just listed of some improvements you could make. All though I'll review after.

Gathros · 2019-01-04T11:52:12Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+#include <stdexcept>
+#include <vector>
+#include <cmath>
+using namespace std;


I don't think the use of using namespace std is a good idea for the philosophy of AAA is. The idea is for the AAA to be used by new comers to the language to learn, also for people to use the algorithm in real work cases and show case the algorithm. I don't believe that using namespace std achieves this.

Gathros · 2019-01-04T11:52:41Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+#include <cmath>
+using namespace std;
+
+class EquationSolver


There really is no need in making a class for solving Gaussian elimination.

So, should I just define each function individually, because I thought encapsulating it would make it more user-friendly and show how it can be used to solve equations.

Gathros · 2019-01-04T11:54:01Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+
+int main() {
+  int varc = 3;
+  vector< vector<long double> > equations { { 2, 3, 4, 6 },


why use long double when double works fine?

Gathros · 2019-01-04T11:54:28Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+  {
+    ans = solver.solveByGaussJordan(equations, varc);
+  }
+  catch(runtime_error &e)


Not a big fan of try catch.

Gathros · 2019-01-04T11:56:37Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+private:
+
+  // subtract row from another row after multiplcation
+  void subRow(vector<long double> &toBeSubtracted, const vector<long double> &toSubtract,


There is no need of making this function if it's used in one place.

Since the row subtraction function was being showcased in the documentation, I thought a special mention would be necessary.

…nctions

Gathros · 2019-01-05T21:11:13Z

Looks much better now. But why is it so different from the C version? Gaussian elimination is not a complex algorithm. I expected it to be the C code with C++ features like std::vector.

rishvic · 2019-01-06T17:46:34Z

I have as of now made some changes, and I do see your point. The main point of difference comes from the fact that I am trying to use the gaussianElimination function to try to find out whether the system of equations is solvable or not. If it's not necessary, then I can remove it.

Gathros · 2019-01-06T17:59:58Z

We are not adding checks into the code. We are assuming the code is correct.

rishvic · 2019-01-06T18:03:29Z

Then I'lll be removing all the parts of code that checks whether the matrix is singular or not.

Gathros · 2019-01-06T19:14:33Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+#include <vector>
+
+
+void gaussianElimination(std::vector< std::vector<double> > &eqns, int varc) {


verc does not need to exist, you can just use int cols = eqns[0].size();.

Gathros · 2019-01-06T19:15:03Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+
+void gaussianElimination(std::vector< std::vector<double> > &eqns, int varc) {
+  // 'eqns' is the matrix, 'varc' is no. of vars
+  int err = 0; // marker for if matrix is singular


you're not using err.

Gathros · 2019-01-06T19:18:10Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+  for (int i = 0; i < varc - 1; i++) {
+    int pivot = i;
+
+    for (int j = i + 1; j < varc; j++)


Put {} on this for loop.

Gathros · 2019-01-06T19:18:46Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+        pivot = j;
+
+    if (eqns[pivot][i] == 0.0) {
+      err = 1; // Marking that matrix is singular


Print "The matrix is singular.\n" here.

Gathros · 2019-01-06T19:21:17Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+    if (i != pivot) // Swapping the rows if new row with higher maxVals is found
+      std::swap(eqns[pivot], eqns[i]); // C++ swap function
+
+    for (int j = i + 1; j < varc; j++) {


j should go to eqns.size() not varc.

Gathros · 2019-01-06T19:45:33Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+}
+
+
+std::vector<double> solveByGaussJordan(std::vector<std::vector<double>> eqns, int varc) {


No need for this function just have this in main.

Gathros · 2019-01-06T19:45:58Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+}
+
+
+std::vector<double> backSubs(std::vector<std::vector<double>> &eqns, int varc)


Again no need for varc.

Gathros · 2019-01-06T19:49:00Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+}
+
+
+std::vector<double> solveByBacksubs(std::vector<std::vector<double>> eqns, int varc) {


No need for this function just have this in main.

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

Gathros · 2019-01-06T19:49:54Z

contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

+  std::vector<double> ans;
+
+  ans = solveByGaussJordan(equations, varc);
+


Print the matrix after the eliminations.

rishvic · 2019-01-07T11:45:53Z

I don't think the gaussian_elimination.md has been synced with my code. So, should I do so right now?

Gathros · 2019-01-07T11:42:45Z

contents/gaussian_elimination/gaussian_elimination.md

+[import:5-13, lang:"c"](code/c/gaussian_elimination.c)
+[import:19-34, lang:"c"](code/c/gaussian_elimination.c)
+{% sample lang="cpp" %}
+[import:25-25, lang:"cpp"](code/c++/gaussian_elimination.cpp)


You don't need this line, everyone know what std::swap does.

Gathros · 2019-01-07T11:44:17Z

contents/gaussian_elimination/gaussian_elimination.md

+[import:19-34, lang:"c"](code/c/gaussian_elimination.c)
+{% sample lang="cpp" %}
+[import:25-25, lang:"cpp"](code/c++/gaussian_elimination.cpp)
+[import:13-25, lang:"cpp"](code/c++/gaussian_elimination.cpp)


Should be import:13-23/

Gathros · 2019-01-07T11:45:54Z

contents/gaussian_elimination/gaussian_elimination.md

-[import:36-41, lang:"c_cpp"](code/c/gaussian_elimination.c)
+[import:36-41, lang:"c"](code/c/gaussian_elimination.c)
+{% sample lang="cpp" %}
+[import:28-32, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)


This should be import:25-32. Also "cpp".

Gathros · 2019-01-07T11:46:52Z

contents/gaussian_elimination/gaussian_elimination.md

-[import:15-48, lang:"c_cpp"](code/c/gaussian_elimination.c)
+[import:15-48, lang:"c"](code/c/gaussian_elimination.c)
+{% sample lang="cpp" %}
+[import:8-36, lang:"cpp"](code/c++/gaussian_elimination.cpp)


import:8-34.

Gathros · 2019-01-07T11:48:02Z

contents/gaussian_elimination/gaussian_elimination.md

-[import:64-82, lang:"c_cpp"](code/c/gaussian_elimination.c)
+[import:64-82, lang:"c"](code/c/gaussian_elimination.c)
+{% sample lang="cpp" %}
+[import:39-53, lang:"cpp"](code/c++/gaussian_elimination.cpp)


import:36-54.

Gathros · 2019-01-07T11:49:03Z

I just remember that.

Added Gaussian Elimimnation in C++

e9527bb

rishvic changed the title ~~"Gaussian Elimimnation" Implementation in C++~~ "Gaussian Elimination" Implementation in C++ Dec 17, 2018

Gathros added the Implementation This provides an implementation for an algorithm. (Code and maybe md files are edited.) label Dec 17, 2018

Modified to upmove the row with highest pivot & added more comments

53dbd1f

Gathros requested changes Jan 4, 2019

View reviewed changes

rishvic added 2 commits January 6, 2019 00:09

Removed the class; Removed 'using namespace std;'; Removed useless fu…

daa272e

…nctions

Resolved conflict with C code in md

08bf7f4

Removed singular matrix checking & made the code simpler

64426a1

Gathros requested changes Jan 6, 2019

View reviewed changes

rishvic added 2 commits January 7, 2019 16:02

Made changes as requested

fbe7bbc

Changed one broken line

70ca766

Gathros approved these changes Jan 7, 2019

View reviewed changes

Gathros requested changes Jan 7, 2019

View reviewed changes

rishvic and others added 2 commits January 7, 2019 17:27

Synced gaussian_elimination.md with cpp code

8ae70e6

Merge branch 'master' into gaussianEliminationInCpp

e04518e

Gathros approved these changes Jan 7, 2019

View reviewed changes

Gathros merged commit 3c38b6f into algorithm-archivists:master Jan 7, 2019

rishvic deleted the gaussianEliminationInCpp branch January 7, 2019 12:04

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"Gaussian Elimination" Implementation in C++ #555

"Gaussian Elimination" Implementation in C++ #555

rishvic commented Dec 17, 2018

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Gathros commented Jan 7, 2019

		#include <vector>


		void gaussianElimination(std::vector< std::vector<double> > &eqns, int varc) {

		}


		std::vector<double> solveByGaussJordan(std::vector<std::vector<double>> eqns, int varc) {

		}


		std::vector<double> backSubs(std::vector<std::vector<double>> &eqns, int varc)

		}


		std::vector<double> solveByBacksubs(std::vector<std::vector<double>> eqns, int varc) {

		std::vector<double> ans;

		ans = solveByGaussJordan(equations, varc);

"Gaussian Elimination" Implementation in C++ #555

"Gaussian Elimination" Implementation in C++ #555

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rishvic commented Dec 17, 2018

rishvic commented Dec 18, 2018

leios commented Dec 23, 2018

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Gathros commented Jan 5, 2019 • edited Loading

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Gathros commented Jan 7, 2019

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