Pca, Principal Components, Dimensionality Reduction, Eigenvectors, Eigenvalue.
Variance-Covariance matrix. Now in this matrix, there are two metrics, variance, and covariance. While calculating these metrics we follow a convention that we tend to ignore because there is nothing special about it. And that convention is using the X-axis and Y-axis as the base, i.e. i^= 0 and j^