Jose Divasón

Formalization and Execution of Linear Algebra: From Theorems to Algorithms

In this work we present a formalization of the Rank Nullity theorem of Linear Algebra in Isabelle/HOL. The formalization is of interest because of various reasons. First, it has been carried out based on the representation of mathematical structures proposed in the HOL Multivariate Analysis library of Isabelle/HOL (which is part of the standard distribution of the proof assistant). Hence, our proof shows the adequacy of such an infrastructure for the formalization of Linear Algebra. Moreover, we enrich the proof with an additional formalization of its computational meaning; to this purpose, we choose to implement the Gauss-Jordan elimination algorithm for matrices over fields, prove it correct, and then apply the Isabelle code generation facility that permits to execute the formalized algorithm. For the algorithm to be code generated, we use again the implementation of matrices available in the HOL Multivariate Analysis library, and enrich it with some necessary features. We report on the precise modifications that we introduce to get code execution from the original representation, and on the performance of the code obtained. We present an alternative verified type refinement of vectors that outperforms the original version. This refinement performs well enough as to be applied to the computation of the rank of some biomedical digital images. Our work proves itself as a suitable basis for the formalization of numerical Linear Algebra in HOL provers that can be successfully applied for computations of real case studies.

A formalization of the Berlekamp-Zassenhaus factorization algorithm

We formalize the Berlekamp–Zassenhaus algorithm for factoring square-free integer polynomials in Isabelle/HOL. We further adapt an existing formalization of Yun’s square-free factorization algorithm to integer polynomials, and thus provide an efficient and certified factorization algorithm for arbitrary univariate polynomials. The algorithm first performs a factorization in the prime field GF(p) and then performs computations in the ring of integers modulo pk, where both p and k are determined at runtime. Since a natural modeling of these structures via dependent types is not possible in Isabelle/HOL, we formalize the whole algorithm using Isabelle’s recent addition of local type definitions. Through experiments we verify that our algorithm factors polynomials of degree 100 within seconds.

Formalisation in higher-order logic and code generation to functional languages of the Gauss-Jordan algorithm

In this paper, we present a formalisation in a proof assistant, Isabelle/HOL, of a naive version of the Gauss-Jordan algorithm, with explicit proofs of some of its applications; and, additionally, a process to obtain versions of this algorithm in two different functional languages (SML and Haskell) by means of code generation techniques from the verified algorithm. The aim of this research is not to compete with specialised numerical implementations of Gausslike algorithms, but to show that formal proofs in this area can be used to generate usable functional programs. The obtained programs show compelling performance in comparison to some other verified and functional versions, and accomplish some challenging tasks, such as the computation of determinants of matrices of big integers and the computation of the homology of matrices representing digital images.

Formalisation of the computation of the echelon form of a matrix in Isabelle/HOL

In this contribution we present a formalised algorithm in the Isabelle/HOL proof assistant to compute echelon forms, and, as a consequence, characteristic polynomials of matrices. We have proved its correctness over Bézout domains, but its executability is only guaranteed over Euclidean domains, such as the integer ring and the univariate polynomials over a field. This is possible since the algorithm has been parameterised by a (possibly non-computable) operation that returns the Bézout coefficients of a pair of elements of a ring. The echelon form is also used to compute determinants and inverses of matrices. As a by-product, some algebraic structures have been implemented (principal ideal domains, Bézout domains, etc.). In order to improve performance, the algorithm has been refined to immutable arrays inside of Isabelle and code can be generated to functional languages as well.

Generalizing a Mathematical Analysis Library in Isabelle/HOL

The HOL Multivariate Analysis Library (HMA) of Isabelle/HOL is focused on concrete types such as \(\mathbb {R}\), \(\mathbb {C}\) and \(\mathbb {R}^n\) and on algebraic structures such as real vector spaces and Euclidean spaces, represented by means of type classes. The generalization of HMA to more abstract algebraic structures is something desirable but it has not been tackled yet. Using that library, we were able to prove the Gauss-Jordan algorithm over real matrices, but our interest lied on generating verified code for matrices over arbitrary fields, greatly increasing the range of applications of such an algorithm. This short paper presents the steps that we did and the methodology that we devised to generalize such a library, which were successful to generalize the Gauss-Jordan algorithm to matrices over arbitrary fields.

A Formalisation in HOL of the Fundamental Theorem of Linear Algebra and Its Application to the Solution of the Least Squares Problem

In this paper we show how a thoughtful reusing of libraries can provide concise proofs of non-trivial mathematical results. Concretely, we formalise in Isabelle/HOL a proof of the Fundamental Theorem of Linear Algebra for vector spaces over inner product spaces, the Gram–Schmidt process of orthogonalising vectors over

Experiences and new alternatives for teaching formal verification of Java programs

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Obtaining an ACL2 Specification from an Isabelle/HOL Theory

R, its application to get the