we derive the formulas of the maximal andminimal ranks of four real matrices $x_{1},x_{2},x_{3}$ and $x_{4}$in common solution $x=x_{1}+x_{2}i+x_{3}j+x_{4}k$ to quaternionmatrix equations $a_{1}x=c_{1},xb_{2}=c_{2},a_{3}xb_{3}=c_{3}$. asapplications, we establish necessary and sufficient conditions forthe existence of the common real and complex solutions to the matrixequations. we give the exp...

begin{abstract}using the fixed point method, we prove the generalized hyers--ulam--rassiasstability of the following functional equation in multi-banach spaces:begin{equation} sum_{ j = 1}^{n}fbig(-2 x_{j} + sum_{ i = 1, ineq j}^{n} x_{i}big) =(n-6) fbig(sum_{ i = 1}^{n} x_{i}big) + 9 sum_{ i = 1}^{n}f(x_{i}).end{equation}end{abstract}

We compare four different estimation methods for the coefficients of a linear structural equation with instrumental variables. As the classical methods we consider the limited information maximum likelihood (LIML) estimator and the two-stage least squares (TSLS) estimator, and as the semi-parametric estimation methods we consider the maximum empirical likelihood (MEL) estimator and the generali...