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Let (,) be an integral kernel, and consider the homogeneous equation, the Fredholm integral equation, (,) =and the inhomogeneous equation (,) = ().The Fredholm alternative is the statement that, for every non-zero fixed complex number, either the first equation has a non-trivial solution, or the second equation has a solution for all ().
The resulting algebraic object satisfies the axioms for a group. Specifically: Associativity The binary operation on G × H is associative. Identity The direct product has an identity element, namely (1 G, 1 H), where 1 G is the identity element of G and 1 H is the identity element of H.
Hilbert (1894) introduced the Hilbert matrix to study the following question in approximation theory: "Assume that I = [a, b], is a real interval.Is it then possible to find a non-zero polynomial P with integer coefficients, such that the integral
Consider the system of equations + + = + + = + + = The coefficient matrix is = [], and the augmented matrix is (|) = []. Since both of these have the same rank, namely 2, there exists at least one solution; and since their rank is less than the number of unknowns, the latter being 3, there are an infinite number of solutions.
In the case of a linear system, the system may be said to be underspecified, in which case the presence of more than one solution would imply an infinite number of solutions (since the system would be describable in terms of at least one free variable [2]), but that property does not extend to nonlinear systems (e.g., the system with the ...
Some sources allow convergence to 0 if there are only a finite number of zero factors and the product of the non-zero factors is non-zero, but for simplicity we will not allow that here. If the product converges, then the limit of the sequence a n as n increases without bound must be 1, while the converse is in general not true.
In less formal terms, the group consists of words in the generators and their inverses, subject only to canceling a generator with an adjacent occurrence of its inverse. If G is any group, and S is a generating subset of G, then every element of G is also of the above form; but in general, these products will not uniquely describe an element of G.
Proof. The equation A X + X B = C {\displaystyle AX+XB=C} is a linear system with m n {\displaystyle mn} unknowns and the same number of equations. Hence it is uniquely solvable for any given C {\displaystyle C} if and only if the homogeneous equation A X + X B = 0 {\displaystyle AX+XB=0} admits only the trivial solution 0 {\displaystyle 0} .