29 November 2025   9:44:19.119 PM
 
fem2d_poisson_cg()
  FORTRAN90 version:
  Solve the Poisson equation using sparse storage
  and a conjugate gradient solver.
 
  Solution of the Poisson equation in an arbitrary region
  in 2 dimensions.
 
  - DEL H(x,y) DEL U(x,y) + K(x,y) * U(x,y) = F(x,y) in the region
 
                    U(x,y) = G(x,y) on the boundary.
 
  The finite element method is used,
  with triangular elements,
  which must be a 3 node linear triangle.
 
  Node file is "ell_nodes.txt".
  Element file is "ell_elements.txt".
  Number of nodes =                65
 
  First 10 nodes
 
  Row         1             2       
  Col
 
    1    0.00000       0.00000    
    2    0.00000      0.500000    
    3   0.500000       0.00000    
    4    0.00000       1.00000    
    5   0.500000      0.500000    
    6    1.00000       0.00000    
    7    0.00000       1.50000    
    8   0.500000       1.00000    
    9    1.00000      0.500000    
   10    1.50000       0.00000    
 
  Element order =                   3
  Number of elements =             96
 
  First 10 elements
 
  Row       1      2      3
  Col
 
    1       1      3      2
    2       6      5      3
    3       4      2      5
    4       3      5      2
    5      23     22     10
    6      21      9     22
    7       6     10      9
    8      22      9     10
    9      19      7     20
   10       4      8      7
 
  Quadrature order =                 3
 
  Number of nonzero coefficients NZ_NUM =      385

  Step        Residual

     1     39.3312    
     2     23.1596    
     3     10.7601    
     4     6.12728    
     5     3.47712    
     6     1.65520    
     7    0.592650    
     8    0.162597    
     9    0.693399E-01
    10    0.241027E-01
    11    0.609233E-02
    12    0.162877E-02
    13    0.299049E-03
    14    0.670415E-04
    15    0.438113E-05

  Number of iterations was   15
  Estimated error is   0.744849E-07
 
  Part of the solution vector U:
 
         1   0.0000000    
         2  0.25000000    
         3  0.25000000    
         4   1.0000000    
         5  0.48493558    
         6   1.0000000    
         7   2.2500000    
         8   1.2289069    
         9   1.2289069    
        10   2.2500000    
 
fem2d_poisson_cg():
  Wrote an ASCII file
    "ell_values.txt"
  of the form
    U ( X(I), Y(I) )
  which can be used for plotting.
 
fem2d_poisson_cg():
  Normal end of execution.
 
29 November 2025   9:44:19.122 PM