Calculus: Early Transcendentals, James Stewart, 2015 (Cengage Learning) - A widely used undergraduate textbook offering coverage of multivariable calculus, including partial derivatives and the gradient vector.
Mathematics for Machine Learning, Marc Peter Deisenroth, A. Aldo Faisal, and Cheng Soon Ong, 2020 (Cambridge University Press)DOI: 10.1017/9781108679989 - A textbook specifically providing the mathematical foundations for machine learning, with explanations of vector calculus and gradients.
Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press) - A comprehensive textbook demonstrating the practical application of the gradient in optimization algorithms for training neural networks.
Multivariable Calculus, Denis Auroux, 2010 (MIT OpenCourseWare) - An MIT OpenCourseWare resource offering lecture videos, notes, and problem sets from a multivariable calculus course covering gradient vectors.