Let H be a real separable Hilbert space and A : D(A) → H be a positive and self-adjoint (unbounded) operator. We consider the identification problem consisting in searching for an H-valued function u and a couple of real numbers λ and μ, the first one being positive, that fulfil the initial-value problem
and the additional constraintsA r/2 u(T ) 2 = ϕ and A s/2 u(T ) 2 = ψ, where we denote by A s and A r the powers of A with exponents r < s. Provided that the given data u 0 ∈ H, u 0 and ϕ, ψ > 0 satisfy proper a priori limitations, by means of a finite-dimensional approximation scheme, we construct a unique solution (u, λ, μ) on the whole interval [0, T ], and exhibit an explicit continuous dependence estimate of Lipschitz type with respect to the data. Also, we provide specific applications to second-and fourth-order parabolic initial-boundary-value problems.