C ++ - why `const type & variable` as function input?

Question

I am converting some functions from Matlab to C ++, and something is related to the matrix. I found this simple function somewhere on the web:

typedef std::vector<std::vector<double> > Matrix;

Matrix sum(const Matrix& a, const Matrix& b) {
  size_t nrows = a.size();
  size_t ncols = a[0].size();
  Matrix c(nrows, std::vector<double>(ncols));
  for (int i = 0; i < nrows; ++i) {
    for (int j = 0; j < ncols; ++j) {
      c[i][j] = a[i][j] + b[i][j];
    }
  }
  return c;
}

Can someone explain to me why they used const Matrix& aas input and not Matrix a? Do they use it as a habit or is there any benefit from using it, since I did not see any difference between the results of the two versions ( const Matrix& aand Matrix aas input).

Answer 1

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Answer 2

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