Basic Mathematics The Laplacian R Horan & M Lavelle The aim of this package is to provide a short self assessment programme for students who want to apply the Laplacian operator. Copyright c 2005
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[email protected] Last Revision Date: April 4, 2005 Version 1.0 Table of Contents 1. Introduction (Grad, Div, Curl) 2. The Laplacian 3. The Laplacian of a Product of Fields 4. The Laplacian and Vector Fields 5. Final Quiz Solutions to Exercises Solutions to Quizzes The full range of these packages and some instructions, should they be required, can be obtained from our web page Mathematics Support Materials. Section 1: Introduction (Grad, Div, Curl) 3 1. Introduction (Grad, Div, Curl) The vector differential operator ∇ , called “del” or “nabla”, is defined in three dimensions to be: ∂ ∂ ∂ ∇ = i + j + k ∂x ∂y ∂z The result of applying this vector operator to a scalar field is called the gradient of the scalar field: ∂f ∂f ∂f gradf(x, y, z) = ∇f(x, y, z) = i + j + k . ∂x ∂y ∂z (See the package on Gradients and Directional Derivatives.) The scalar product of this vector operator with a vector field F (x, y, z) is called the divergence of the vector field: ∂F ∂F ∂F divF (x, y, z) = ∇ · F = 1 + 2 + 3 . ∂x ∂y ∂z Section 1: Introduction (Grad, Div, Curl) 4 The vector product of the vector ∇ with a vector field F (x, y, z) is the curl of the vector field. It is written as curl F (x, y, z) = ∇ × F ∂F ∂F ∂F ∂F ∂F ∂F ∇ × F (x, y, z) = ( 3 − 2 )i − ( 3 − 1 )j + ( 2 − 1 )k ∂y ∂z ∂x ∂z ∂x ∂y i j k ∂ ∂ ∂ = , ∂x ∂y ∂z F1 F2 F3 where the last line is a formal representation of the line above.