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rishvicrishvic
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Removed the class; Removed 'using namespace std;'; Removed useless functions
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-155
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‎contents/gaussian_elimination/code/c++/gaussian_elimination.cpp

Lines changed: 118 additions & 149 deletions
Original file line numberDiff line numberDiff line change
@@ -1,187 +1,156 @@
1-
#include <iostream>
21
#include <algorithm>
2+
#include <cmath>
3+
#include <iostream>
34
#include <stdexcept>
45
#include <vector>
5-
#include <cmath>
6-
using namespace std;
7-
8-
class EquationSolver
9-
{
10-
private:
11-
12-
// subtract row from another row after multiplcation
13-
void subRow(vector<long double> &toBeSubtracted, const vector<long double> &toSubtract,
14-
long double mult, int start)
15-
{
16-
for (int i = start; i < toBeSubtracted.size(); i++)
17-
toBeSubtracted[i] -= mult * toSubtract[i];
18-
}
19-
// A start variable is given since if we know all values are 0, we don't need
20-
// to subtract.
216

227

23-
// swap two rows
24-
void swapRow(vector<long double> &eqn1, vector<long double> &eqn2, int start)
25-
{
26-
for (int i = start; i < eqn1.size(); i++)
27-
swap(eqn1[i], eqn2[i]);
28-
}
29-
// A start variable is given since if we know all values are 0, we don't need
30-
// to swap.
31-
32-
33-
int gaussianElimination(vector<vector<long double>> &eqns, int varc)
34-
{
35-
// 'eqns' is the matrix, 'varc' is no. of vars
36-
int err = 0; // marker for if matrix is singular
37-
for (int i = 0; i < varc - 1; i++)
38-
{
39-
long double pivot = fabsl(eqns[i][i]);
40-
int newRow = i;
41-
for (int j = i + 1; j < varc; j++)
42-
{
43-
if (fabsl(eqns[j][i]) > pivot)
44-
{
45-
pivot = fabsl(eqns[j][i]);
46-
newRow = j;
47-
}
48-
}
8+
int gaussianElimination(std::vector< std::vector<double> > &eqns, int varc) {
9+
// 'eqns' is the matrix, 'varc' is no. of vars
10+
int err = 0; // marker for if matrix is singular
11+
for (int i = 0; i < varc - 1; i++) {
12+
double pivot = fabs(eqns[i][i]);
13+
int newRow = i;
4914

50-
if (pivot == 0.0)
51-
{
52-
err = 1; // Marking that matrix is singular
53-
continue;
15+
for (int j = i + 1; j < varc; j++) {
16+
if (fabs(eqns[j][i]) > pivot) {
17+
pivot = fabs(eqns[j][i]);
18+
newRow = j;
5419
}
55-
if (newRow != i)
56-
swapRow(eqns[newRow], eqns[i], i);
57-
58-
for (int j = i + 1; j < varc; j++)
59-
if (eqns[j][i])
60-
subRow(eqns[j], eqns[i], (eqns[j][i] / eqns[i][i]), i);
6120
}
6221

63-
if (eqns[varc - 1][varc - 1] == 0 || err)
64-
{
65-
if (eqns[varc - 1][varc] == 0 || err)
66-
return 1; // Error code: Singular matrix
67-
else
68-
return 2; // Error code: No solutions
69-
// Cannot solve since final equation is '0*xn = c'
22+
if (pivot == 0.0) {
23+
err = 1; // Marking that matrix is singular
24+
continue;
7025
}
71-
return 0; // Successful
72-
}
7326

27+
if (newRow != i) // Swapping the rows if new row with higher pivot is found
28+
std::swap(eqns[newRow], eqns[i]); // C++ swap function
7429

75-
void gaussJordan(vector<vector<long double>> &eqns, int varc)
76-
{
77-
// 'eqns' is the (Row-echelon) matrix, 'varc' is no. of vars
78-
for (int i = varc - 1; i >= 0; i--)
79-
{
80-
eqns[i][varc] /= eqns[i][i];
81-
eqns[i][i] = 1; // We know that the only entry in this row is 1
82-
83-
for (int j = i - 1; j >= 0; j--) // subtracting rows from below
84-
{
85-
eqns[j][varc] -= eqns[j][i] * eqns[i][varc];
86-
eqns[j][i] = 0; // We also set all the other values in row to 0 directly
87-
}
30+
for (int j = i + 1; j < varc; j++) {
31+
if (eqns[j][i]) {
32+
double mult = eqns[j][i] / eqns[i][i];
33+
eqns[j][i] = 0.0;
34+
for (int k = i + 1; k < (varc + 1); k++) // k doesn't start at 0, since
35+
eqns[j][k] -= mult * eqns[i][k]; // values before from 0 to i
36+
} // are already 0
8837
}
8938
}
9039

40+
if (eqns[varc - 1][varc - 1] == 0 || err) {
41+
if (eqns[varc - 1][varc] == 0 || err)
42+
return 1; // Error code: Singular matrix
43+
else
44+
return 2; // Error code: No solutions
45+
// Cannot solve since final equation is '0*xn = c'
46+
}
47+
48+
return 0; // Successful
49+
}
50+
9151

92-
vector<long double> backSubs(vector<vector<long double>> &eqns, int varc)
93-
{
94-
// 'eqns' is matrix, 'varc' is no. of variables
95-
vector<long double> ans(varc);
96-
for (int i = varc - 1; i >= 0; i--)
97-
{
98-
long double sum = 0;
99-
for (int j = i + 1; j < varc; j++)
100-
sum += eqns[i][j] * ans[j];
52+
void gaussJordan(std::vector< std::vector<double> > &eqns, int varc) {
53+
// 'eqns' is the (Row-echelon) matrix, 'varc' is no. of vars
54+
for (int i = varc - 1; i >= 0; i--) {
55+
eqns[i][varc] /= eqns[i][i];
56+
eqns[i][i] = 1; // We know that the only entry in this row is 1
10157

102-
ans[i] = (eqns[i][varc] - sum) / eqns[i][i];
58+
// subtracting rows from below
59+
for (int j = i - 1; j >= 0; j--) {
60+
eqns[j][varc] -= eqns[j][i] * eqns[i][varc];
61+
eqns[j][i] = 0; // We also set all the other values in row to 0 directly
10362
}
104-
return ans;
10563
}
64+
}
65+
10666

107-
public:
108-
vector<long double> solveByGaussJordan(vector< vector<long double> > eqns, int varc)
109-
{
110-
int status = this->gaussianElimination(eqns, varc);
111-
switch (status)
112-
{
113-
case 0:
114-
break;
67+
std::vector<double> backSubs(std::vector<std::vector<double>> &eqns, int varc)
68+
{
69+
// 'eqns' is matrix, 'varc' is no. of variables
70+
std::vector<double> ans(varc);
71+
for (int i = varc - 1; i >= 0; i--) {
72+
double sum = 0;
73+
for (int j = i + 1; j < varc; j++)
74+
sum += eqns[i][j] * ans[j];
75+
76+
ans[i] = (eqns[i][varc] - sum) / eqns[i][i];
77+
}
78+
return ans;
79+
}
11580

116-
case 1:
117-
throw runtime_error("Singular matrix");
11881

119-
case 2:
120-
throw runtime_error("No solutions");
121-
}
82+
std::vector<double> solveByGaussJordan(std::vector<std::vector<double>> eqns, int varc) {
83+
int status = gaussianElimination(eqns, varc);
84+
switch (status) {
85+
case 0:
86+
break;
12287

123-
this->gaussJordan(eqns, varc);
88+
case 1:
89+
std::cout << "Singular matrix" << std::endl;
90+
return std::vector<double>(0); // return empty vector in case of no solutions
12491

125-
vector<long double> ans(varc);
126-
for (int i = 0; i < varc; i++)
127-
ans[i] = eqns[i][varc];
128-
return ans;
92+
case 2:
93+
std::cout << "No solutions" << std::endl;
94+
return std::vector<double>(0); // return empty vectors in case of no solutions
12995
}
13096

131-
vector<long double> solveByBacksubs(vector< vector<long double> > eqns, int varc)
132-
{
133-
int status = this->gaussianElimination(eqns, varc);
134-
switch (status)
135-
{
136-
case 0:
137-
break;
97+
gaussJordan(eqns, varc);
13898

139-
case 1:
140-
throw runtime_error("Singular matrix");
99+
std::vector<double> ans(varc);
100+
for (int i = 0; i < varc; i++)
101+
ans[i] = eqns[i][varc];
102+
return ans;
103+
}
141104

142-
case 2:
143-
throw runtime_error("No solutions");
144-
}
145105

146-
vector<long double> ans = this->backSubs(eqns, varc);
147-
return ans;
106+
std::vector<double> solveByBacksubs(std::vector<std::vector<double>> eqns, int varc) {
107+
int status = gaussianElimination(eqns, varc);
108+
switch (status) {
109+
case 0:
110+
break;
111+
112+
case 1:
113+
std::cout << "Singular matrix" << std::endl;
114+
return std::vector<double>(0); // return empty vectors in case of no solutions
115+
116+
case 2:
117+
std::cout << "No solutions" << std::endl;
118+
return std::vector<double>(0); // return empty vectors in case of no solutions
148119
}
149-
};
120+
121+
std::vector<double> ans = backSubs(eqns, varc);
122+
return ans;
123+
}
124+
150125

151126
int main() {
152127
int varc = 3;
153-
vector< vector<long double> > equations { { 2, 3, 4, 6 },
154-
{ 1, 2, 3, 4 },
155-
{ 3, -4, 0, 10 }};
156-
EquationSolver solver;
157-
vector<long double> ans;
158-
try
159-
{
160-
ans = solver.solveByGaussJordan(equations, varc);
161-
}
162-
catch(runtime_error &e)
163-
{
164-
cout << "Error found: " << e.what() << endl;
165-
return -1;
128+
std::vector< std::vector<double> > equations{
129+
{2, 3, 4, 6},
130+
{1, 2, 3, 4},
131+
{3, -4, 0, 10}};
132+
133+
std::vector<double> ans;
134+
135+
ans = solveByGaussJordan(equations, varc);
136+
137+
if (ans.empty()) { // If ans is empty, then no unique solutions exist
138+
std::cout << "No solution" << std::endl;
139+
} else {
140+
std::cout << "The solution is (by Gauss Jordan)," << std::endl
141+
<< "x == " << ans[0] << std::endl
142+
<< "y == " << ans[1] << std::endl
143+
<< "z == " << ans[2] << std::endl;
166144
}
167145

168-
cout << "The solution is (by Gauss-Jordan)," << endl
169-
<< "x == " << ans[0] << endl
170-
<< "y == " << ans[1] << endl
171-
<< "z == " << ans[2] << endl << endl;
146+
ans = solveByBacksubs(equations, varc);
172147

173-
try
174-
{
175-
ans = solver.solveByBacksubs(equations, varc);
148+
if (ans.empty()) { // If ans is empty, then no unique solutions exist
149+
std::cout << "No solution" << std::endl;
150+
} else {
151+
std::cout << "The solution is (by Backsubstitution)," << std::endl
152+
<< "x == " << ans[0] << std::endl
153+
<< "y == " << ans[1] << std::endl
154+
<< "z == " << ans[2] << std::endl;
176155
}
177-
catch (runtime_error &e)
178-
{
179-
cout << "Error found: " << e.what() << endl;
180-
return -1;
181-
}
182-
183-
cout << "The solution is (by Backsubstitution)," << endl
184-
<< "x == " << ans[0] << endl
185-
<< "y == " << ans[1] << endl
186-
<< "z == " << ans[2] << endl;
187156
}

‎contents/gaussian_elimination/gaussian_elimination.md

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -315,8 +315,8 @@ In code, this process might look like this:
315315
[import:5-13, lang:"c_cpp"](code/c/gaussian_elimination.c)
316316
[import:19-34, lang:"c_cpp"](code/c/gaussian_elimination.c)
317317
{% sample lang="cpp" %}
318-
[import:23-30, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
319-
[import:36-56, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
318+
[import:27-28, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
319+
[import:12-28, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
320320
{% sample lang="hs" %}
321321
[import:10-17, lang:"haskell"](code/haskell/gaussianElimination.hs)
322322
[import:44-46, lang:"haskell"](code/haskell/gaussianElimination.hs)
@@ -388,7 +388,7 @@ Here is what it might look like in code:
388388
{% sample lang="c" %}
389389
[import:36-41, lang:"c_cpp"](code/c/gaussian_elimination.c)
390390
{% sample lang="cpp" %}
391-
[import:12-20, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
391+
[import:32-35, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
392392
{% sample lang="hs" %}
393393
[import:19-33, lang:"haskell"](code/haskell/gaussianElimination.hs)
394394
[import:42-42, lang:"haskell"](code/haskell/gaussianElimination.hs)
@@ -409,7 +409,7 @@ When we put everything together, it looks like this:
409409
{% sample lang="c" %}
410410
[import:15-48, lang:"c_cpp"](code/c/gaussian_elimination.c)
411411
{% sample lang="cpp" %}
412-
[import:12-72, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
412+
[import:8-49, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
413413
{% sample lang="rs" %}
414414
[import:41-78, lang:"rust"](code/rust/gaussian_elimination.rs)
415415
{% sample lang="hs" %}
@@ -448,7 +448,7 @@ Here it is in code:
448448
{% sample lang="c" %}
449449
[import:64-82, lang:"c_cpp"](code/c/gaussian_elimination.c)
450450
{% sample lang="cpp" %}
451-
[import:75-89, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
451+
[import:52-64, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
452452
{% sample lang="rs" %}
453453
This code does not exist yet in rust, so here's Julia code (sorry for the inconvenience)
454454
[import:67-93, lang:"julia"](code/julia/gaussian_elimination.jl)
@@ -491,7 +491,7 @@ In code, it looks like this:
491491
{% sample lang="c" %}
492492
[import:50-62, lang:"c_cpp"](code/c/gaussian_elimination.c)
493493
{% sample lang="cpp" %}
494-
[import:92-105, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
494+
[import:67-79, lang:"c_cpp"](code/c++/gaussian_elimination.cpp)
495495
{% sample lang="rs" %}
496496
[import:79-94, lang:"rust"](code/rust/gaussian_elimination.rs)
497497
{% sample lang="hs" %}

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