FEM2D_PACK
Finite Element Routines

FEM2D_PACK is a FORTRAN77 library which can help in implementing the finite element method.

The emphasis is on simplicity and clarity. Primarily, the 2D planar case is handled, with a choice of low order triangular ("T") and quadrilateral ("Q") elements.

A few routines are included for computing a "sphere grid", that is, a finite element mesh on the surface of a sphere.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

FEM2D_PACK is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

FEM_BASIS, a FORTRAN77 library which can define basis functions for the finite element method (FEM) for any degree in an M-dimensional simplex (1D interval, 2D triangle, 3D tetrahedron, and higher dimensional generalizations.)

FEM2D, a data directory which contains examples of 2D FEM files, three text files that describe a 2D finite element geometry;

FEM2D_HEAT, a FORTRAN90 program which solves the 2D time dependent heat equation on the unit square.

FEM2D_POISSON, a FORTRAN90 program which solves the 2D Poisson equation on a square, using the finite element method.

FEM2D_SAMPLE, a FORTRAN77 library which evaluates a finite element function defined on an order 3 or order 6 triangulation.

MESH_BANDWIDTH, a FORTRAN77 program which returns the geometric bandwidth associated with a mesh of elements of any order and in a space of arbitrary dimension.

Reference:

1. Milton Abramowitz, Irene Stegun,
   Handbook of Mathematical Functions,
   National Bureau of Standards, 1964,
   ISBN: 0-486-61272-4,
   LC: QA47.A34.
2. Jack Dongarra, Jim Bunch, Cleve Moler, Pete Stewart,
   LINPACK User's Guide,
   SIAM, 1979,
   ISBN13: 978-0-898711-72-1.
3. Vladimir Krylov,
   Approximate Calculation of Integrals,
   Dover, 2006,
   ISBN: 0486445798.
4. Hans Rudolf Schwarz,
   Finite Element Methods,
   Academic Press, 1988,
   ISBN: 0126330107,
   LC: TA347.F5.S3313.
5. Gilbert Strang, George Fix,
   An Analysis of the Finite Element Method,
   Cambridge, 1973,
   ISBN: 096140888X,
   LC: TA335.S77.
6. Arthur Stroud,
   Approximate Calculation of Multiple Integrals,
   Prentice Hall, 1971,
   ISBN: 0130438936,
   LC: QA311.S85.
7. Arthur Stroud, Don Secrest,
   Gaussian Quadrature Formulas,
   Prentice Hall, 1966,
   LC: QA299.4G3S7.
8. Olgierd Zienkiewicz,
   The Finite Element Method,
   Sixth Edition,
   Butterworth-Heinemann, 2005,
   ISBN: 0750663200,
   TA640.2.Z54
9. Daniel Zwillinger, editor,
   CRC Standard Mathematical Tables and Formulae,
   30th Edition,
   CRC Press, 1996,
   ISBN: 0-8493-2479-3.

Source Code:

• fem2d_pack.f, the source code;
• fem2d_pack.sh, commands to compile the source code.

Examples and Tests:

• fem2d_pack_prb.f, the calling program;
• fem2d_pack_prb.sh, commands to compile, link and run the calling program;
• fem2d_pack_prb_output.txt, the output file.
• fem2d_pack_prb_q4.png, a PNG image of a Q4 mesh.
• fem2d_pack_prb_t3.png, a PNG image of a T3 mesh.
• fem2d_pack_prb_t4.png, a PNG image of a T4 mesh.
• fem2d_pack_prb_t6.png, a PNG image of a T6 mesh.
• sphere_q4_nodes.txt, a node file for a Q4 mesh, which is also a polygonal surface, that approximates a sphere.
• sphere_q4_elements.txt, an element file for a Q4 mesh, which is also a polygonal surface, that approximates a sphere.
• sphere_q9_nodes.txt, a node file for a Q9 mesh that approximates a sphere.
• sphere_q9_elements.txt, an element file for a Q9 mesh that approximates a sphere.
• sphere_q16_nodes.txt, a node file for a Q16 mesh that approximates a sphere.
• sphere_q16_elements.txt, an element file for a Q16 mesh that approximates a sphere.
• sphere_t3_nodes.txt, a node file for a T3 mesh, which is also a polygonal surface, that approximates a sphere.
• sphere_t3_elements.txt, an element file for a T3 mesh, which is also a polygonal surface, that approximates a sphere.
• sphere_t6_nodes.txt, a node file for a T6 mesh that approximates a sphere.
• sphere_t6_elements.txt, an element file for a T6 mesh that approximates a sphere.

List of Routines:

• BANDWIDTH_MESH: bandwidth of finite element mesh.
• BANDWIDTH_VAR determines the bandwidth for finite element variables.
• BASIS_11_Q4: one basis at one point for a Q4 element.
• BASIS_11_Q4_TEST verifies BASIS_11_Q4.
• BASIS_11_T3: one basis at one point for the T3 element.
• BASIS_11_T3_TEST verifies BASIS_11_T3.
• BASIS_11_T4: one basis at one point for a T4 element.
• BASIS_11_T4_TEST verifies BASIS_11_T4.
• BASIS_11_T6: one basis at one point for the T6 element.
• BASIS_11_T6_TEST verifies BASIS_11_T6.
• BASIS_MN_Q4: all bases at N points for a Q4 element.
• BASIS_MN_Q4_TEST verifies BASIS_MN_Q4.
• BASIS_MN_T3: all bases at N points for a T3 element.
• BASIS_MN_T3_TEST verifies BASIS_MN_T3.
• BASIS_MN_T4: all bases at N points for a T4 element.
• BASIS_MN_T4_TEST verifies BASIS_MN_T4.
• BASIS_MN_T6: all bases at N points for a T6 element.
• BASIS_MN_T6_TEST verifies BASIS_MN_T6.
• CH_CAP capitalizes a single character.
• DEGREES_TO_RADIANS converts an angle measure from degrees to radians.
• DERIVATIVE_AVERAGE_T3 averages derivatives at the nodes of a T3 mesh.
• DERIVATIVE_AVERAGE_T6 averages derivatives at the nodes of a T6 mesh.
• DIV_Q4 estimates the divergence and vorticity of a discrete field.
• ELEMENT_CODE returns the code for each element.
• GET_UNIT returns a free FORTRAN unit number.
• GRID_NODES_01 returns an equally spaced rectangular grid in the unit square.
• GRID_PRINT prints the elements that form a grid.
• GRID_WIDTH computes the width of a given grid.
• I4_MODP returns the nonnegative remainder of integer division.
• I4_WRAP forces an I4 to lie between given limits by wrapping.
• I4MAT_WRITE writes an I4MAT file.
• I4VEC_PRINT prints an I4VEC.
• INTERP interpolates a quantity in an element from basis node values.
• LEGENDRE_DR_COMPUTE: Gauss-Legendre quadrature by Davis-Rabinowitz method.
• LEGENDRE_SET sets abscissas and weights for Gauss-Legendre quadrature.
• MASS_MATRIX_T3 computes the mass matrix, using 3-node triangles.
• MASS_MATRIX_T6 computes the mass matrix, using 6-node triangles.
• NEXT_BOUNDARY_NODE returns the next boundary node in any element.
• NEXT_BOUNDARY_NODE_Q4 returns the next boundary node in a Q4 element.
• NEXT_BOUNDARY_NODE_Q8 returns the next boundary node in a Q8 element.
• NEXT_BOUNDARY_NODE_Q9 returns the next boundary node in a Q9 element.
• NEXT_BOUNDARY_NODE_Q12 returns the next boundary node in a Q12 element.
• NEXT_BOUNDARY_NODE_Q16 returns the next boundary node in a Q16 element.
• NEXT_BOUNDARY_NODE_QL returns the next boundary node in a QL element.
• NEXT_BOUNDARY_NODE_T3 returns the next boundary node in a T3 element.
• NEXT_BOUNDARY_NODE_T4 returns the next boundary node in a T4 element.
• NEXT_BOUNDARY_NODE_T6 returns the next boundary node in a T6 element.
• NEXT_BOUNDARY_NODE_T10 returns the next boundary node in a T10 element.
• NODE_REFERENCE returns the basis nodes for any available element.
• NODE_REFERENCE_Q4 returns the basis nodes for a 4 node quadrilateral.
• NODE_REFERENCE_Q8 returns the basis nodes for an 8 node quadrilateral.
• NODE_REFERENCE_Q9 returns the basis nodes for a 9 node quadrilateral.
• NODE_REFERENCE_Q12 returns the basis nodes for a 12 node quadrilateral.
• NODE_REFERENCE_Q16 returns the basis nodes for a 16 node quadrilateral.
• NODE_REFERENCE_QL returns the basis nodes for a quadratic/linear.
• NODE_REFERENCE_T3 returns the basis nodes for the 3 node triangle.
• NODE_REFERENCE_T4 returns the basis nodes for the 4 node triangle.
• NODE_REFERENCE_T6 returns the basis nodes for a 6 node triangle.
• NODE_REFERENCE_T10 returns the basis nodes for a 10 node triangle.
• NS_T6_VAR_COUNT counts the Navier Stokes variables on a T6 grid.
• NS_T6_VAR_SET sets the Navier Stokes variables on a T6 grid.
• ORDER_CODE returns the order for each element.
• PHYSICAL_TO_REFERENCE_T3 maps physical points to reference points.
• POLY returns the polynomial terms associated with any available element.
• POLY_Q4 returns the monomials associated with a 4 node quadrilateral.
• POLY_Q8 returns the monomials associated with an 8 node quadrilateral.
• POLY_Q9 returns the monomials associated with a 9 node quadrilateral.
• POLY_Q12 returns the monomials associated with a 12 node quadrilateral.
• POLY_Q16 returns the monomials associated with a 16 node quadrilateral.
• POLY_QL returns the monomials for a quadratic/linear quadrilateral.
• POLY_T3 returns the monomials associated with a 3 node triangle.
• POLY_T6 returns the monomials associated with a 6 node triangle.
• POLY_T10 returns the monomials associated with a 10 node triangle.
• R8_HUGE returns a "huge" R8.
• R8_POWER computes the P-th power of an R8.
• R8_SWAP switches two R8's.
• R8_UNIFORM_01 returns a unit pseudorandom R8.
• R8GE_FA performs a LINPACK style PLU factorization of an R8GE matrix.
• R8GE_INVERSE computes the inverse of a matrix factored by R8GE_FA.
• R8MAT_PRINT prints an R8MAT.
• R8MAT_PRINT_SOME prints some of an R8MAT.
• R8MAT_WRITE writes a R8MAT file.
• R8VEC_DOT_PRODUCT finds the dot product of a pair of R8VEC's.
• R8VEC_SUM sums the entries of an R8VEC.
• REFERENCE_SAMPLE samples a reference element.
• REFERENCE_TO_PHYSICAL_Q4 maps Q4 reference points to physical points.
• REFERENCE_TO_PHYSICAL_T3 maps T3 reference points to physical points.
• REFERENCE_TO_PHYSICAL_T6 maps T6 reference points to physical points.
• S_EQI is a case insensitive comparison of two strings for equality.
• SHAPE evaluates shape functions for any available reference element.
• SHAPE_Q4 evaluates shape functions for a 4 node reference quadrilateral.
• SHAPE_Q8 evaluates shape functions for an 8 node reference quadrilateral.
• SHAPE_Q9 evaluates shape functions for a 9 node reference quadrilateral.
• SHAPE_Q12 evaluates shape functions for a 12 node reference quadrilateral.
• SHAPE_Q16 evaluates shape functions for a 16 node reference quadrilateral.
• SHAPE_QL evaluates shape functions for a 6 node quadratic/linear.
• SHAPE_T3 evaluates shape functions for a 3 node reference triangle.
• SHAPE_T4 evaluates shape functions for a 4 node reference triangle.
• SHAPE_T6 evaluates shape functions for a 6 node reference triangle.
• SHAPE_T10 evaluates shape functions for a 10 node reference triangle.
• SHAPE_TEST verifies the shape function values at the basis nodes.
• TIMESTAMP prints out the current YMDHMS date as a timestamp.
• TRIANGLE_UNIT_SET sets a quadrature rule in the unit triangle.
• TRIANGLE_UNIT_SIZE returns the "size" of a unit triangle quadrature rule.

You can go up one level to the FORTRAN77 source codes.