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如何检查两个矩阵是否相同?

eigen c++14 matrix c++11 c++

KcFnMi · 技术社区 · 8 年前

想法是把两个矩阵相乘。用本征做同样的乘法,然后检查结果是否相同。

在下面的制作过程中 N = 2 退货 same thing 但是 N = 1000 退货 NOT same thing . 为什么?

#include <cstdlib>
#include <iostream>
#include <Eigen/Dense>

using namespace std;
using namespace Eigen;

const int N = 1000;

void mult_matrix(double x[N][N], double y[N][N], double z[N][N]) {
    int rows = N;
    int cols = N;
    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            for (int k = 0; k < cols; k++)
                z[i][j] += x[i][k] * y[k][j];
}

void check(double *x, double *y, double *z) {

    Matrix<double, Dynamic, Dynamic, RowMajor> m = 
            Matrix<double, Dynamic, Dynamic, RowMajor>::Map(x, N, N) * 
            Matrix<double, Dynamic, Dynamic, RowMajor>::Map(y, N, N);

    cout << m(0, 0) << endl;
    cout << Matrix<double, Dynamic, Dynamic, RowMajor>::Map(z, N, N)(0, 0) << endl;

    if (m == Matrix<double, Dynamic, Dynamic, RowMajor>::Map(z, N, N))
        cout << "same thing" << endl;
    else
        cout << "NOT same thing" << endl;
}

int main() {
    double *a = (double*)malloc(N*N*sizeof(double));
    double *b = (double*)malloc(N*N*sizeof(double));
    double *c = (double*)malloc(N*N*sizeof(double));

    Matrix<double, Dynamic, Dynamic, RowMajor>::Map(a, N, N).setRandom();
    Matrix<double, Dynamic, Dynamic, RowMajor>::Map(b, N, N).setRandom();
    Matrix<double, Dynamic, Dynamic, RowMajor>::Map(c, N, N).setZero();

    mult_matrix((double (*)[N])a, (double (*)[N])b, (double (*)[N])c);
    check(a, b, c);
}

4 回复 | 直到 8 年前

RHertel 8 年前

isApprox()

==

if (m.isApprox(Matrix<double, Dynamic, Dynamic, RowMajor>::Map(z, N, N)))
  cout << "same thing" << endl;
else
  cout << "NOT same thing" << endl;

isMuchSmallerThan()

Daniel Heilper 8 年前

== N=2 N

bool double_equals(double a, double b, double epsilon = 0.001)
{
    return std::abs(a - b) < epsilon;
}

double reldiff(double a, double b) {
    double divisor = fmax(fabs(a), fabs(b)); /* If divisor is zero, both x and y are zero, so the difference between them is zero */
    if (divisor == 0.0) return 0.0; return fabs(a - b) / divisor; 
}

bool double_equals(double a, double b, double rel_diff)
{
    return reldiff(a, b) < rel_diff;
}

Yves Daoust 8 年前

0.1 0.99999999999993 0.100000000000002

|a - b| < max(|a|, |b|).Îµ

Îµ 10^-7

(sin(1.000001) - sin(1)) / 0.000001 = (0.84147104 - 0.84147100) / 0.0000001 = 0.40000000 0.5403023

Yves Daoust 8 年前

u = 2^-t t n n u < 0.01 xTy

1.01 n u |x|T |y|

xTy = 0