SymEigenValues

This function calculates eigenvalues of a symmetric matrix.

note

• For n=2 it calls SymEigenValues2y2
• For n=3 it calls SymEigenValues3by3
• For n>=4 it calls SYEV routine from Lapack95

܀ Interface

INTERFACE
  MODULE FUNCTION SymEigenValues(mat) RESULT(ans)
    REAL(DFP), INTENT(IN) :: mat(:, :)
    !! for n=2, we call SymEigenValues2by2
    !! for n=3, we call SymEigenValues3by3
    !! for n>=4, we call Lapack or JacobiMethod
    REAL(DFP) :: ans(SIZE(mat, 1))
  END FUNCTION SymEigenValues
END INTERFACE

️܀ See example

PROGRAM main
USE easifemBase
	REAL( DFP ), ALLOCATABLE :: mat(:,:), w(:), exact(:)
	REAL( DFP ), PARAMETER :: tol= 1.0E-2
	
	mat =RESHAPE( &
		[   1.96, -6.49, -0.47, -7.20, -0.65, &
			& -6.49, 3.80, -6.39, 1.50, -6.34, &
			& -0.47,-6.39, 4.17, -1.51, 2.67, &
			& -7.20, 1.50,-1.51, 5.70, 1.80, &
			& -0.65,-6.34, 2.67, 1.80,-7.10 &
		], [5,5])
	!!
	w = SymEigenValues(mat)
	!!
	exact = [-11.07, -6.23, 0.86, 8.87, 16.09]
	!!
	CALL OK( ALL(SOFTEQ(w, exact, tol)), "")
END PROGRAM main

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