In mathematics, a P-matrix is a complex square matrix with every principal minor is positive. A closely related class is that of -matrices, which are the closure of the class of P-matrices, with every principal minor 0.
By a theorem of Kellogg, the eigenvalues of P- and - matrices are bounded away from a wedge about the negative real axis as follows:
If are the eigenvalues of an n-dimensional P-matrix, where , then
If , , are the eigenvalues of an n-dimensional -matrix, then
The class of nonsingular M-matrices is a subset of the class of P-matrices. More precisely, all matrices that are both P-matrices and Z-matrices are nonsingular M-matrices. The class of sufficient matrices is another generalization of P-matrices.
The linear complementarity problem has a unique solution for every vector q if and only if M is a P-matrix. This implies that if M is a P-matrix, then M is a Q-matrix.
If the Jacobian of a function is a P-matrix, then the function is injective on any rectangular region of .
A related class of interest, particularly with reference to stability, is that of -matrices, sometimes also referred to as -matrices. A matrix A is a -matrix if and only if is a P-matrix (similarly for -matrices). Since , the eigenvalues of these matrices are bounded away from the positive real axis.
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In mathematics, the class of Z-matrices are those matrices whose off-diagonal entries are less than or equal to zero; that is, the matrices of the form: Note that this definition coincides precisely with that of a negated Metzler matrix or quasipositive matrix, thus the term quasinegative matrix appears from time to time in the literature, though this is rare and usually only in contexts where references to quasipositive matrices are made. The Jacobian of a competitive dynamical system is a Z-matrix by definition.