Check out example codes for "matrix multiplication c++ eigen". It will help you in understanding the concepts better.

Code Example 1

```
MatrixXcf a = MatrixXcf::Random(2,2);
cout << "Here is the matrix a\n" << a << endl;
cout << "Here is the matrix a^T\n" << a.transpose() << endl;
```

Code Example 2

```
Matrix2d mat;
mat << 1, 2,
3, 4;
std::cout << "Here is mat*mat:\n" << mat*mat << std::endl;
```

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