Also found in: Dictionary, Thesaurus, Wikipedia.
principal diagonal[′prin·sə·pəl dī′ag·ən·əl]
For a square matrix, the diagonal extending from the upper left-hand corner to the lower right-hand corner of the matrix, that is, the diagonal containing the elements aij for which i = j. Also known as main diagonal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.