Least-Squares Solution of Linear Differential Equations. Mortari, D. Mathematics, 5(4):48, December, 2017.
Least-Squares Solution of Linear Differential Equations [link]Paper  doi  abstract   bibtex   1 download  
This study shows how to obtain least-squares solutions to initial value problems (IVPs), boundary value problems (BVPs), and multi-value problems (MVPs) for nonhomogeneous linear differential equations (DEs) with nonconstant coefficients of any order. However, without loss of generality, the approach has been applied to second-order DEs. The proposed method has two steps. The first step consists of writing a constrained expression, that has the DE constraints embedded. These kind of expressions are given in terms of a new unknown function, g ( t ) , and they satisfy the constraints, no matter what g ( t ) is. The second step consists of expressing g ( t ) as a linear combination of m independent known basis functions. Specifically, orthogonal polynomials are adopted for the basis functions. This choice requires rewriting the DE and the constraints in terms of a new independent variable, x ∈ [ − 1 , + 1 ] . The procedure leads to a set of linear equations in terms of the unknown coefficients of the basis functions that are then computed by least-squares. Numerical examples are provided to quantify the solutions’ accuracy for IVPs, BVPs and MVPs. In all the examples provided, the least-squares solution is obtained with machine error accuracy.
@article{mortari2017a,
	title = {Least-{Squares} {Solution} of {Linear} {Differential} {Equations}},
	volume = {5},
	copyright = {http://creativecommons.org/licenses/by/3.0/},
	issn = {2227-7390},
	url = {https://www.mdpi.com/2227-7390/5/4/48},
	doi = {10.3390/math5040048},
	abstract = {This study shows how to obtain least-squares solutions to initial value problems (IVPs), boundary value problems (BVPs), and multi-value problems (MVPs) for nonhomogeneous linear differential equations (DEs) with nonconstant coefficients of any order. However, without loss of generality, the approach has been applied to second-order DEs. The proposed method has two steps. The first step consists of writing a constrained expression, that has the DE constraints embedded. These kind of expressions are given in terms of a new unknown function,     g ( t )    , and they satisfy the constraints, no matter what     g ( t )     is. The second step consists of expressing     g ( t )     as a linear combination of m independent known basis functions. Specifically, orthogonal polynomials are adopted for the basis functions. This choice requires rewriting the DE and the constraints in terms of a new independent variable,     x ∈ [ − 1 , + 1 ]    . The procedure leads to a set of linear equations in terms of the unknown coefficients of the basis functions that are then computed by least-squares. Numerical examples are provided to quantify the solutions’ accuracy for IVPs, BVPs and MVPs. In all the examples provided, the least-squares solution is obtained with machine error accuracy.},
	language = {en},
	number = {4},
	urldate = {2024-04-24},
	journal = {Mathematics},
	author = {Mortari, Daniele},
	month = dec,
	year = {2017},
	keywords = {embedded linear constraints, interpolation, linear least-squares},
	pages = {48},
}

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