SetTriDiag

SetTriDiag routine can be used for setting the three diagonals (main, sub diagonal, superdiagonal) of a square dense matrix.

The generic call is given below.

CALL SetTriDiag( mat, d, da, db)

where,

• mat(:,:) is a square matrix of Real(DFP)
• d(:) is a vector of Real32 | Real64 | Int8 | Int16 | Int32 | Int64, and it stands for main diagonal
• If size of d is 1, then it means the diagonal values are constant, otherwise the size of d should be same as the main diagonal of matrix mat.
• da(:) is a vector ofReal32 | Real64 | Int8 | Int16 | Int32 | Int64`, and it stands for first superdiagonal. Its size should be (n-1).
• db(:) is a vector ofReal32 | Real64 | Int8 | Int16 | Int32 | Int64`, and it stands for first subdiagonal. Its size should be (n-1).

️܀ Example

In this example we show the usage of SetTriDiag routine.

We will set the three diagonal of a tridiagonal matrix.

header

program main
  use easifemBase

variables

  real( DFP ), allocatable :: mat(:, :)
  real( DFP ), allocatable :: d(:), da(:), db(:)

form main diagonal

  mat = zeros(5,5,1.0_DFP)
  call reallocate(d, size(mat,1))
  call random_number(d)
  d = d * 10
  call display( MdEncode(d), "d = "// CHAR_LF )

super diagonal

  call reallocate(da, size(mat,1)-1)
  call random_number(da)
  da = da * 10
  call display( MdEncode(da), "da = "// CHAR_LF )

subdigonal

  call reallocate(db, size(mat,1)-1)
  call random_number(db)
  db = db * 10
  call display( MdEncode(db), "db = "// CHAR_LF )

set tridiagonal

  call SetTriDiag(mat=mat, d=d, da=da, db=db)
  call Display( MdEncode(mat), "mat = " // CHAR_LF)

Results

d =

5.0829	9.4562	4.3419	7.7858	3.9234

da =

4.9034	3.8319	0.60738	5.3554

db =

4.7704	0.58276	7.87791E-02	8.1903

mat =

5.0829	4.9034	0	0	0
4.7704	9.4562	3.8319	0	0
0	0.58276	4.3419	0.60738	0
0	0	7.87791E-02	7.7858	5.3554
0	0	0	8.1903	3.9234

cleanup

end program

↢