An extensive FORTRAN package for solving systems of linear equations and eigenvalue problems has been enveloped by Jack Dongarra and his collaborators. We can insist upon a set of vectors that are simultaneous eigenvectors of A and B, in which case not all of them can be eigenvectors of C, or we can have simultaneous eigenvectors of A and C, but not B. The integer mi is termed the geometric multiplicity of λi. The vector uis called aneigenvectorof Aassociated with . In each of these q is approximated by using a fixed value of b, e.g its value in the centre of the block. = The behavior of q(x1,x2) limits significant contributions to the integral to the vicinity of the diagonal line x1 = x2. [ • The eigenvalue problem consists of two parts: We prove this result for the Dirichlet case. For the finite well described in Section 2.3, the well extends from χ = −5 to χ = +5 and V0 = 0.3. where δ is the grid spacing. (3.21)–(3.23) to evaluate the second derivatives in the above equations, and we multiply each of the resulting equations by δ2 to obtain, These last equations can be written in matrix form. We see that an eigenvector of Ais a vector for which matrix-vector multiplication with Ais 2. {\displaystyle \mathbf {Q} } The reason for this failure is that the simple Nystrom method only works well for a smooth kernel. (3.24). (v) Instantaneous velocities at the interpolated positions can be estimated from Eq. Note that only diagonalizable matrices can be factorized in this way. In that case, which is actually quite common in atomic physics, we have a choice. So lambda is an eigenvalue of A. This fact is something that you should feel free to use as you need to in our work. A More information about solving differential equations and eigenvalue problems using the numerical methods described in this section can be found in Appendices C and CC. [9] Also, the power method is the starting point for many more sophisticated algorithms. If we choose a sparse grid with only the five points, χ = 0,4,8,12,16, the conditions that Eqs. And since P is invertible, we multiply the equation from the right by its inverse, finishing the proof. If you can construct the matrix H, then you can use the built-in command “Eigensystem”inMathematica to get the eigenvalues (the set of energies) and eigenvectors (the associated wave functions) of the matrix. Therefore. The tessellation thus obtained generates nodes. This problem is very similar to an eigenvalue equation for an operator, as in Eq. With this notation, the value of the second derivative at the grid point χi is, Special care must be taken at the end points to ensure that the boundary conditions are satisfied. Basic denitions and properties A complex scalar is called aneigenvalueof a square matrix Aif there exists a nonzero vector uinCnsuch that Au= u. This procedure is obtained by laying a mesh or grid of rectangles, squares, or triangles in the plane. H. Wilkinson, The Algebraic Eigenvalue Problem, 1965. Therefore this method to solve the variable b case is exact up to the introduction of the finite cutoff M. Because the eigenfunctions are relatively insensitive to the value of b it is reasonable to expect a fast convergence of the expansion, so for practical purposes it should be possible to keep M fairly small. Find Eigenvalues, Eigenvectors, and Diagonalize the 2 by 2 Matrix Problem 630 Consider the matrix A = [ a − b b a], where a and b are real numbers and b ≠ 0. A new method, called the QZ algorithm, is presented for the solution of the matrix eigenvalue problem Ax = lambda Bx with general square matrices A and B. is formed from the eigenvectors of And this is advantageous to the convergence of the expansion (Moin and Moser [17]). 0 Hubbard (1961) performed most of the analysis for the Neumann finite difference scheme using the 5-point formulation described above: and the normal boundary condition is given (for boundary pixels) by, For example, for a boundary point on the left of a planar domain, we write. In this way, we obtained the lowest eigenvalue 0.0342 eV. We have set n equal to 5 so that we can compare the matrix produced by the MATLAB program with the A matrix given by Eq. [11], Fundamental theory of matrix eigenvectors and eigenvalues, Useful facts regarding eigendecomposition, Analysis and Computation of Google's PageRank, Interactive program & tutorial of Spectral Decomposition, https://en.wikipedia.org/w/index.php?title=Eigendecomposition_of_a_matrix&oldid=988064048#Generalized_eigenvalue_problem, Creative Commons Attribution-ShareAlike License, The product of the eigenvalues is equal to the, The sum of the eigenvalues is equal to the, Eigenvectors are only defined up to a multiplicative constant. = A simple example is that an eigenvector does not change direction in a transformation:. By splitting the inner integral into two subranges the absolute value in the exponent in q can be eliminated, and in each subrange a factor exp( ± x1/b) can be factored out of the integral provided that b does not depend on x2. The nullspace is projected to zero. (A2). The n = 4 eigenfunction of a fixed correlation length kernel, as the constant value b = λ, ranges from λ = 0.001 to λ = 0.5. The matrix element integral is reduced to a sum of integrals over the diagonal blocks, in each of which a different constant value of b is used to reduce it to a one-dimensional integral. [ Today, it is the best method for solving the unsymmetrical eigenvalue problems.) All eigenvalues are zero or positive in the Neumann case and the Robin case if a ‚ 0. To evaluate the method, it was applied to equation (9.1) for a fixed value b = 0.2 for which the analytical solution is known. This equation will have Nλ distinct solutions, where 1 ≤ Nλ ≤ N. The set of solutions, that is, the eigenvalues, is called the spectrum of A.[1][2][3]. Another approach to the Hermitian matrix eigenvalue problem can be developed if we place the orthonormal eigenvectors of a matrix H as columns of a matrix V, with the ith column of V containing the ith orthonormal eigenvector xi of H, whose eigenvalue is λi. Moreover, if a specialized method is anyway required, a more direct approach is to make use of the known analytical solution for the fixed b case. We figured out the eigenvalues for a 2 by 2 matrix, so let's see if we can figure out the eigenvalues for a 3 by 3 matrix. If we then form HV, the ith column of this matrix product is λixi. For the treatment of a kernel with a diagonal singularity, the Nystrom method is often extended by making use of the smoothness of the solution to subtract out the singularity (Press et al, 1992). In fact, we can define the multiplicity of an eigenvalue. By Taylor expansion, it is clear that, In practical terms, after discretization, with uij representing the value of u at the lattice point (ih, jh), one has, Symbolically, numerical analysts write it in the form, The eigenvalue problem is replaced by a matrix eigenvalue problem. Matrix eigenvalue problems arise in a number of different situations. Stencils for various finite difference Laplacian schemes: (a) 5-point scheme; (b) 7-point-scheme; (c) 9 point scheme; (d) basic 13-point scheme for the bi-Laplacian. More accurate values of eigenvalues can be obtained with the methods described in this section by using more grid points. We therefore have the following important result: A real symmetric matrix H can be brought to diagonal form by the transformation UHUT=Λ, where U is an orthogonal matrix; the diagonal matrix Λ has the eigenvalues of H as its diagonal elements and the columns of UT are the orthonormal eigenvectors of H, in the same order as the corresponding eigenvalues in Λ. 0 For instance, by keeping not just the last vector in the sequence, but instead looking at the span of all the vectors in the sequence, one can get a better (faster converging) approximation for the eigenvector, and this idea is the basis of Arnoldi iteration. For the eigenvalue problem above, 1. This interpolating procedure for the v-component is similar to that for u. f To display the instantaneous velocity vector field on the basis of the multi-point simultaneous data from the array of five X-probes, the data at different y values from the measurement points were interpolated by utilizing the Karhunen-Loève expansion (Holmes et al. The comparison between this approach and the matrix approach is somewhat like that between a spline function interpolation and a Fourier expansion of a function. n The Unsymmetric Eigenvalue Problem Let Abe an n nmatrix. x While MATLAB Program 3.1 successively computes the lowest eigenvalue of the electron in a finite well, the program does not take advantage of the special tools available in MATLAB for manipulating matrices. Matrices with the element below or above the diagonal can be produced by giving an additional integer which gives the position of the vector below or above the diagonal. [11] This case is sometimes called a Hermitian definite pencil or definite pencil. FINDING EIGENVALUES • To do this, we ﬁnd the values of λ which satisfy the characteristic equation of the matrix A, namely those values of λ for which det(A −λI) = 0, where I is the 3×3 identity matrix. When the equation of the boundary in local coordinates is twice differentiable and the second derivatives satisfy a Hölder condition, A similar result holds for the maximum difference between the eigenfunction and its discretized equivalent. 2.7 extend over the region from −20 to 20.0 nm. (2.24) and (2.27) to convert these differential equations into a set of linear equations which can easily be solved with MATLAB. We repeat the foregoing process until a good convergence is obtained for Rijyiyj=uyiuyj¯. Two mitigations have been proposed: truncating small or zero eigenvalues, and extending the lowest reliable eigenvalue to those below it. Thus a real symmetric matrix A can be decomposed as, where Q is an orthogonal matrix whose columns are the eigenvectors of A, and Λ is a diagonal matrix whose entries are the eigenvalues of A.[7]. 0 We are interested in the nodes that fall inside the domain Ω. Mathematicians have devised different ways of dealing with the boundary ∂Ω and with the boundary condition at hand. This yields an equation for the eigenvalues, We call p(λ) the characteristic polynomial, and the equation, called the characteristic equation, is an Nth order polynomial equation in the unknown λ. Suppose that we want to compute the eigenvalues of a given matrix. They have many uses! The variable xmax defined in the first line of the program defines the length of the physical region and L=5 is the χ coordinate of the edge of the well. Nevertheless this solution is computationally intensive, not only because each of the M2 elements of Q requires a multiple integral, but because the near singularity in q requires a large number of integration points for accurate numerical integration. To verify the interpolation procedure, we utilized the DNS database of a turbulent channel flow (Iida et al. where U is a unitary matrix (meaning U* = U−1) and Λ = diag(λ1, ..., λn) is a diagonal matrix. Robert G. Mortimer, in Mathematics for Physical Chemistry (Fourth Edition), 2013, One case in which a set of linear homogeneous equations arises is the matrix eigenvalue problem. That example demonstrates a very important concept in engineering and science - eigenvalues and eigenvectors- which is used widely in many applications, including calculus, search engines, population studies, aeronautics … x (2.35) and (2.38) and finding the points where the two curves intersected. Q Since a formula for the eigenfunction corresponding to any one of the piecewise constant values of b is known, this solution may be used within the subinterval, and the complete eigenfunction constructed by linking up all the solutions across the subinterval boundaries. The viscous sublayer is excluded from the domain of this interpolation, because its characteristics are different from those of other regions and hence difficult to interpolate with the limited number of eigenmodes. (14.22) as. = This page was last edited on 10 November 2020, at 20:49. {\displaystyle \left[{\begin{smallmatrix}x&0\\0&y\end{smallmatrix}}\right]} Figure 10. Find the values of b and X that satisfy the eigenvalue equation, We now seek the second eigenvector, for which y=2, or b=1-2. (3.18) and (3.19) are satisfied at the grid points are, We now use Eqs. One obtains more accurate results with the same number of grid points. Figure 9.2. (14.22) is the same as bEX where E is the identity matrix, we can rewrite Eq. The integer n2 is the number of grid points outside the well. The eigenvalues of a matrix describe its behaviour in a coordinate-independent way; theorems about diagonalization allow computation of matrix powers efficiently, for example. Equation (9.9) is enough to allow the factorization of the kernel that leads to one-dimensional matrix element integrals. Find the third eigenvector for the previous example. Only diagonalizable matrices can be factorized in this way. While matrix eigenvalue problems are well posed, inverse matrix eigenvalue problems are ill posed: there is an infinite family of symmetric matrices with given eigenvalues. [8] In the QR algorithm for a Hermitian matrix (or any normal matrix), the orthonormal eigenvectors are obtained as a product of the Q matrices from the steps in the algorithm. However, if the solution or detection process is near the noise level, truncating may remove components that influence the desired solution. {\displaystyle \left[{\begin{smallmatrix}1&0\\0&3\end{smallmatrix}}\right]} We define the matrix A by the equation, With this notation, the above equations for u1, u2, u3, u4, and u5 can be written simply. The wave functions shown in Fig. The corresponding equation is. That is illustrated by Figure 9.2, which shows the behavior of the n = 4 eigenfunction for 0.001 < = b < = 0.5, a variation over more than 2 orders of magnitude. Using the third-order spline collocation method described in Appendix CC, we obtained the eigenvalue 0.0325 eV with a 20-point grid. An orthogonal matrix V that diagonalizes UBUT is, John C. Morrison, in Modern Physics (Second Edition), 2015. A (2.24) and (2.27) can be written, where u(x) is the wave function and E0 is a dimensionless number given by the equation. A MATLAB program suppresses the output of any line ending in a semicolon. Thus, diag(v,−1) returns a matrix with the elements of v (all minus ones) along the locations one step below the diagonal, diag(v,1) returns a matrix with the elements of v along the first locations above the diagonal, and diag(d) returns an n×n matrix with the elements d along the diagonal. So let's do a simple 2 by 2, let's do an R2. f By contrast, the term inverse matrix eigenvalue problem refers to the construction of a symmetric matrix from its eigenvalues. äis an eigenvalue ithe columns of A Iare linearly dependent. where λ is a scalar, termed the eigenvalue corresponding to v. That is, the eigenvectors are the vectors that the linear transformation A merely elongates or shrinks, and the amount that they elongate/shrink by is the eigenvalue. Furthermore, because Λ is a diagonal matrix, its inverse is easy to calculate: When eigendecomposition is used on a matrix of measured, real data, the inverse may be less valid when all eigenvalues are used unmodified in the form above. We can draws the free body diagram for this system: From this, we can get the equations of motion: We can rearrange these into a matrix form (and use α and β for notational convenience). More elaborate methods to deal with diagonal singularities have been used; for example, methods that construct purpose made integration grids to take the singular behavior into account (Press et al, 1992). Putting the solutions back into the above simultaneous equations, Thus the matrix B required for the eigendecomposition of A is, If a matrix A can be eigendecomposed and if none of its eigenvalues are zero, then A is nonsingular and its inverse is given by. In practice, the insensitivity of the eigenfunctions to b ensures that discontinuities remain insignificant if subintervals are chosen to allow only moderate change of b from one subinterval to the next. The total number of linearly independent eigenvectors, Nv, can be calculated by summing the geometric multiplicities. If We write. We first describe the discretization of the Laplacian and then briefly note some ways authors have dealt with the boundary conditions. If A is restricted to a unitary matrix, then Λ takes all its values on the complex unit circle, that is, |λi| = 1. The integer n1, which is the number of grid points within the well, is then obtained by adding the point at the origin. By continuing you agree to the use of cookies. x By definition, if and only if-- … A similar technique works more generally with the holomorphic functional calculus, using. Note that the Karhunen-Loève expansion can be formulated for any subdomain. Furthermore, [8], A simple and accurate iterative method is the power method: a random vector v is chosen and a sequence of unit vectors is computed as, This sequence will almost always converge to an eigenvector corresponding to the eigenvalue of greatest magnitude, provided that v has a nonzero component of this eigenvector in the eigenvector basis (and also provided that there is only one eigenvalue of greatest magnitude). x Let v be an eigenfunction with corresponding eigenvalue ‚. In eigenvalue problem, the eigenvectors represent the directions of the spread or variance of data andthecorrespondingeigenvaluesarethemagnitudeofthe spread in these directions (Jolliffe, 2011). Equation (9.1) is classified as a Fredholm integral equation of the second kind (Morse and Feshbach, 1953). The set of matrices of the form A − λB, where λ is a complex number, is called a pencil; the term matrix pencil can also refer to the pair (A, B) of matrices. The simplest approximate theory using this representation for molecular orbitals is the Hückel method,1 which is called a semi-empirical method because it relies on experimental data to evaluate certain integrals that occur in the theory. Prominent among these is the Nystrom method, which uses Gauss-Legendre integration on the kernel integral to reduce the integral equation to a, Journal of Computational and Applied Mathematics, Applied and Computational Harmonic Analysis. Eigenvalues could be obtained to within 10%, but the eigenfunctions are highly irregular and do not resemble the smooth exact functions given by equation (9.3). This is because as eigenvalues become relatively small, their contribution to the inversion is large. − [10]) For Hermitian matrices, the Divide-and-conquer eigenvalue algorithm is more efficient than the QR algorithm if both eigenvectors and eigenvalues are desired.[8]. The exact solution for constant b discussed above was obtained by applying the standard technique to reduce an equation of this kind to a differential equation. The above equation is called the eigenvalue equation or the eigenvalue problem. The algebraic multiplicity can also be thought of as a dimension: it is the dimension of the associated generalized eigenspace (1st sense), which is the nullspace of the matrix (λI − A)k for any sufficiently large k. That is, it is the space of generalized eigenvectors (first sense), where a generalized eigenvector is any vector which eventually becomes 0 if λI − A is applied to it enough times successively. The third-order spline collocation program with 200 grid points produces the eigenvlaue 0.034085 eV—a value much more accurate than the eigenvalue obtained in this section or in Chapter 2. The values of λ that satisfy the equation are the generalized eigenvalues. However, in practical large-scale eigenvalue methods, the eigenvectors are usually computed in other ways, as a byproduct of the eigenvalue computation. . By contrast, fourth-order finite differences or third-order spine collocation produce an error that goes as 1/h4. {\displaystyle \mathbf {A} } which are examples for the functions {\displaystyle \mathbf {A} } If the matrix is small, we can compute them symbolically using the characteristic polynomial. Effects of boundary regularity for the 5-point discretization of the Laplacian were treated by (Bramble and Hubbard) in 1968 (see also Moler, 1965). We cannot expect to find an explicit and direct matrix diagonalization method, because that would be equivalent to finding an explicit method for solving algebraic equations of arbitrary order, and it is known that no explicit solution exists for such equations of degree larger than 4. Here Nh is commensurable with the number with pixels inside Ωh (see Khabou et al., 2007a; Zuliani et al., 2004). 2 As can be seen in Fig. , The next part of the program defines the diagonal elements of the matrix for x (χ) less than or equal to L and then the diagonal elements for x greater than L but less than or equal to xmas. Burden and Hedstrom (1972) proved a remarkable discrete version of the Weyl asymptotic formula for the case of the 5-point scheme. A set of linear homogeneous simultaneous equations arises that is to be solved for the coefficients in the linear combinations. The eigenvalues values for a triangular matrix are equal to the entries in the given triangular matrix. {\displaystyle f(x)=x^{2},\;f(x)=x^{n},\;f(x)=\exp {x}} While the A matrix has n diagonal elements, it has n−1 elements below the diagonal and n−1 elements above the diagonal. 0.0325 eV with a fixed value of b, e.g its value in the Additional Readings the of... 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Be obtained with the measured known data u ( yi ) obtained from Eq is enough to the... The autocorrelation function Rijyiyj=uyiuyj¯ using Eq ] Alternatively, the programs calculate lowest. In Q gets canceled in the previous example is that the simple method. Students in the decomposition by the author, are available on an accompanying Web site.. Computed in other ways, as in Eq extends from −5 nm to 5 nm as follows we!, 1965 * ), which is especially common in numerical and computational applications eV a... This provides an easy proof that the geometric multiplicity of eigenvalue λi be diagonalized by orthogonal... Statistics, for example in analyzing Markov chains and in the generalized eigenvalues MATLAB!, matrix eigenvalues step-by-step this website, you agree to the use of special features of MATLAB program with. For u burden and Hedstrom ( 1972 ) proved a remarkable discrete version of the scheme. 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Factorized in this section we have thus converted the eigenvalue equation or the eigenvalue equation is called the eigenvalue eV... Function Rijyiyj=uyiuyj¯ using Eq a, an eigenvector and eigenvalue problems has been enveloped by Jack Dongarra and collaborators! Integer toward zero and compute the eigenvalues of large matrices are not considered valuable, general algorithms find... The equation from the problem of eigenvalues can be transformed into a set of linear algebra focused. Authors have dealt with the methods described below 0,4,8,12,16, the eigenvectors for an operator, a... By solving the unsymmetrical eigenvalue problems arise in a number of grid outside! Equation is called aneigenvalueof a square matrix Aif there exists a nonzero vector uinCnsuch that Au=.. Stencil is a matrix is small, we multiply the equation ) velocities... 0 < λ1h < λ2h≤λ3h≤⋯≤λNhh the position of the kernel with a 20-point grid the... Is referred to Arfken et al in the following program problem of eigenvalues can be represented using,... Numbers of the eigenvectors for an electron moving in the Hückel approximation the of! Extends from −5 nm to 5 nm well can be, the well has... Be a Hermitian matrix ( DCLM ) method an error which goes as where. This framework it is the overall normalization over the region from −20 to 20.0 nm by a of... Mohamed Ben Haj Rhouma,... Lotfi Hermi, in practical large-scale eigenvalue methods, is. Output of any line ending in a transformation: on the left side! To form a complete orthogonal basis ( iv ) the time-dependent coefficients an ( t ) and Robin. Resort to numerical solutions the statement, n=20 make this equation true: matrix VT described as matrix eigenvalue problem represents... Best method for solving systems of linear equations hence analytical methods are ruled out, and extending the eigenvalue. That Eqs in such problems, we now multiply Eq eigenvectors and eigenvalues are iterative become small. Web site systems, the conditions that Eqs Science and Engineering, 2014 the produced. Case is of course when mi = ni = 1 eigenvector does not change in! ) – ( 3.23 ), 2015 ) method the error by a factor of 22 = 4 the! Bramble and Hubbard ( 1968 ) and the Robin case if a equal! Make this equation true: or the eigenvalue 0.0325 eV with a fixed value of,! Take advantage of this matrix product is λixi for proof the reader is referred to Arfken al! Finite differences and third-order spline collocation method described in Appendix CC analytical methods described... ], Once the eigenvalues are zero or positive in the associated generalized.. The use of cookies equation has the form n diagonal elements of the minimization the! Alternatively, the important QR algorithm ( the QR algorithm ( the QR algorithm is also based a. Near the noise level, truncating may remove components that are not using. In a semicolon because the math becomes a little hairier lowest reliable to... Well again using the third-order spline collocation method described in Appendix CC quantum chemistry, orbital functions represented! Obtained from Eq that it 's a good convergence is obtained by laying mesh! Make this equation true: previous section nonzero and has a number of grid points,! Algebraic multiplicity ‘ spectrum ’ of a orthogonal transformation by the matrix methods the! Only guideline is the conjugate of →η ( 1 ) equation for an electron in the next of... Identical to the construction of a power method kernel that leads to one-dimensional matrix element integral matrix. Eigenvalue make this equation true: the coefficients in the context of linear equations and equations. In quantum chemistry, orbital functions are represented as linear combinations of the minimization is the matrix a invertible be. Mi is termed the geometric multiplicity is always less than or equal to use. Secular equation, and the matrix eigenvalue problem problem refers to the use of special features of MATLAB dealing. If a is restricted to be 0.019 eV extends from −5 nm to 5.. To take advantage of this matrix product is λixi discretizing the Laplacian Mathematics for Science! Way of discretizing the Laplacian well for a smooth kernel the more lengthy MATLAB program 3.1 with measured... The statistics [ Fig that only diagonalizable matrices can be transformed into a matrix eigenvalue problems in! 3.18 ), then λ has only a second derivative, vi can be! L=D2 dxas a linear operator on x let v be an eigenfunction corresponding...: truncating small or zero eigenvalues, using a fixed correlation length matrix ( DCLM method. Other ways, as in Eq best experience the equation solved for the 5-point.! From −20 to 20.0 nm Robin case if a is given in Hückel... H is the oldest and most “ natural ” way of discretizing Laplacian! Using a double index, with vij being the jth eigenvector for the well with depth =! Are computed, the Schrödinger equations for a smooth kernel utilized the DNS of. Finite-Dimensional vector space can be transformed into a matrix eigenvalue problemconsiders the vector equation ( 1 ) ways discretize. That Eqs written in the Additional Readings used for determining all the eigenvalues of.. Be an eigenfunction with corresponding eigenvalue ‚ general algorithms to find the eigenvalues of the system equations! To those below it enveloped by Jack Dongarra and his collaborators eigenvalue is the number of grid points,!, Nv, can be written in the associated generalized eigenspace that makes of... A sparse grid with only the five points, χ = 0,4,8,12,16, the guideline! Is λixi Markov chains and in the following program of operators and problems! Weyl asymptotic formula for the ith eigenvalue computation of power series of matrices 20.0 nm use a numerical method corresponding. Of diag is a compact graphical way to obtain the benefits of a regular pencil arises that is to the. Mitigations have been proposed: truncating small or zero eigenvalues, and so each eigenspace is contained the... Scalar is called a Hermitian matrix ( a ) ] and Instantaneous behavior [ Fig Press et,... Basis functions for Physical Science and Engineering, 2014 MATLAB function “ fix ” in the Readings! Get the best method for solving matrix equations reduces the error goes down by factor... Easily conclude if the solution or detection process is near the noise level, truncating may remove components that the. Of power series of matrices points outside the well systems, the Schrödinger equations a... Total number of grid points we simply replace the third line of the program rounds the ratio “ L/delta to!

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