Added examples.

Author: loiseaujc

example/specialmatrices/example_specialmatrices_dp_spmv.f90

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+program example_tridiagonal_matrix
+   use stdlib_constants, only: dp
+   use stdlib_specialmatrices
+   implicit none
+
+   integer, parameter :: n = 5
+   type(Tridiagonal_dp_type) :: A
+   real(dp) :: dl(n), dv(n), du(n)
+   real(dp) :: x(n), y(n), y_dense(n)
+
+   ! Create an arbitrary tridiagonal matrix.
+   dl = [(i, i=1, n - 1)]; dv = [(2*i, i=1, n)]; du = [(3*i, i=1, n)]
+   A = Tridiagonal(dl, dv, du)
+
+   ! Initialize vectors.
+   x = 1.0_dp; y = 0.0_dp; y_dense = 0.0_dp
+
+   ! Perform matrix-vector products.
+   call spmv(A, x, y)
+   y_dense = matmul(dense(A), x)
+
+   print *, 'dense       :', y_dense
+   print *, 'Tridiagonal :', y
+
+end program example_tridiagonal_matrix

example/specialmatrices/example_tridiagonal_dp_type.f90

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+program example_tridiagonal_matrix
+   use stdlib_constants, only: dp
+   use stdlib_specialmatrices
+   implicit none
+
+   integer, parameter :: n = 5
+   type(Tridiagonal_dp_type) :: A
+   real(dp) :: dl(n), dv(n), du(n)
+
+   ! Generate random tridiagonal elements.
+   call random_number(dl)
+   call random_number(dv)
+   call random_number(du)
+
+   ! Create the corresponding Tridiagonal matrix.
+   A = Tridiagonal(dl, dv, du)
+
+end program example_tridiagonal_matrix