Using raw c style matrix in Eigen

Question

Is there an easy way to wrap a double** in a c++ Eigen typ so that it can be used in Eigen expressions? As far as I know, the Eigen::Map class only supports double*. The storage where double** points to is not guaranteed to be continuous.

Answer 1

正如您所指出的，您可以使用Eigen::Map来包装连续的数据：

double *data = new...
Map<MatrixXd> mappedData(data, m, n);
mappedData.transposeInPlace(); // etc.

非连续数据必须连续成为copy in an Eigen object，或连续double*并使用上述Map。

修改

您不能使用（映射/换行）非连续内存部分作为Eigen :: Matrix。如果您可以控制内存分配，则可以执行以下操作：

// make contiguous data array; better yet, make an
// Eigen::VectorXd of the same size to ensure alignment
double *actualData = new double[m*n]; 
double **columnPointers = new double[n];
for(int i = 0; i < n; ++i) columnPointers[i] = actualData + i * m;
... // do whatever you need to do with the double**
Map<MatrixXd> mappedData(actualData, m, n);
... // send to ceres, or whatever