A matrix differential equation is a differential equation in which the unknown is a function whose values are matrices. A first-order linear matrix differential equation has the form
It is equivalent to a coupled system of scalar ordinary differential equations for the entries of . When
, a nonsingular solution
is called a solution matrix, and every solution of the corresponding
vector differential equation can then
be written
.
For a constant matrix , the initial value problem
has solution , given by a matrix
exponential.