Cramer's rule: Difference between revisions
→{{header|C sharp}}
Line 213:
-4.000
1.000</pre>
=={{header|C++}}==
{{trans|C#}}
<lang cpp>#include <algorithm>
#include <iostream>
#include <vector>
class SubMatrix {
const std::vector<std::vector<double>> *source;
std::vector<double> replaceColumn;
const SubMatrix *prev;
size_t sz;
int colIndex = -1;
public:
SubMatrix(const std::vector<std::vector<double>> &src, const std::vector<double> &rc) : source(&src), replaceColumn(rc), prev(nullptr), colIndex(-1) {
sz = replaceColumn.size();
}
SubMatrix(const SubMatrix &p) : source(nullptr), prev(&p), colIndex(-1) {
sz = p.size() - 1;
}
SubMatrix(const SubMatrix &p, int deletedColumnIndex) : source(nullptr), prev(&p), colIndex(deletedColumnIndex) {
sz = p.size() - 1;
}
int columnIndex() const {
return colIndex;
}
void columnIndex(int index) {
colIndex = index;
}
size_t size() const {
return sz;
}
double index(int row, int col) const {
if (source != nullptr) {
if (col == colIndex) {
return replaceColumn[row];
} else {
return (*source)[row][col];
}
} else {
if (col < colIndex) {
return prev->index(row + 1, col);
} else {
return prev->index(row + 1, col + 1);
}
}
}
double det() const {
if (sz == 1) {
return index(0, 0);
}
if (sz == 2) {
return index(0, 0) * index(1, 1) - index(0, 1) * index(1, 0);
}
SubMatrix m(*this);
double det = 0.0;
int sign = 1;
for (size_t c = 0; c < sz; ++c) {
m.columnIndex(c);
double d = m.det();
det += index(0, c) * d * sign;
sign = -sign;
}
return det;
}
};
std::vector<double> solve(SubMatrix &matrix) {
double det = matrix.det();
if (det == 0.0) {
throw new std::runtime_error("The determinant is zero.");
}
std::vector<double> answer(matrix.size());
for (int i = 0; i < matrix.size(); ++i) {
matrix.columnIndex(i);
answer[i] = matrix.det() / det;
}
return answer;
}
std::vector<double> solveCramer(const std::vector<std::vector<double>> &equations) {
int size = equations.size();
if (std::any_of(
equations.cbegin(), equations.cend(),
[size](const std::vector<double> &a) { return a.size() != size + 1; }
)) {
throw new std::runtime_error("Each equation must have the expected size.");
}
std::vector<std::vector<double>> matrix(size);
std::vector<double> column(size);
for (int r = 0; r < size; ++r) {
column[r] = equations[r][size];
matrix[r].resize(size);
for (int c = 0; c < size; ++c) {
matrix[r][c] = equations[r][c];
}
}
SubMatrix sm(matrix, column);
return solve(sm);
}
template<typename T>
std::ostream &operator<<(std::ostream &os, const std::vector<T> &v) {
auto it = v.cbegin();
auto end = v.cend();
os << '[';
if (it != end) {
os << *it++;
}
while (it != end) {
os << ", " << *it++;
}
return os << ']';
}
int main() {
std::vector<std::vector<double>> equations = {
{ 2, -1, 5, 1, -3},
{ 3, 2, 2, -6, -32},
{ 1, 3, 3, -1, -47},
{ 5, -2, -3, 3, 49},
};
auto solution = solveCramer(equations);
std::cout << solution << '\n';
return 0;
}</lang>
{{out}}
<pre>[2, -12, -4, 1]</pre>
=={{header|C sharp}}==
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