Corrections to “An Efficient Preconditioner for 3D Finite Difference Modeling of the Electromagnetic Diffusion Process in the Frequency Domain” [DOI: 10.1109/TGRS.2019.2937742]

A label of an equation in the Four-Color Cellblock Gauss-Seidel Preconditioner section of the title article contains a writing mistake, so we are modifying it by: 1) changing “violation of (8)” to “violation of (6)” and 2) changing “free condition in (8)” to “free condition in (6).” This error does not affect the text or results presented in the article.