FEM1D_PROJECT
Project Data onto a 1D Finite Element Mesh

FEM1D_PROJECT is a FORTRAN77 program which computes the projection of sample data onto a given finite element mesh.

This procedure can be used to determine the least squares approximant to data (actually, to the piecewise linear interpolant of that data) or to determine the finite element coefficients appropriate when recomputing a finite element solution from a fine mesh to a coarse mesh.

The sample data is given simply as two files, one containing the points, the other, the corresponding data values.

The user must also supply two files defining the finite element mesh, containing the points, and the pairs of points that form the elements.

The program takes the sample data, projects it onto the finite element mesh, and determines a file of finite element coefficients that represent the projection of the data onto the finite element space.

The current version of the program can only handle finite element meshes which are made of piecewise linear basis functions.

Usage:

fem1d_project sample_prefix fem_prefix

• sample_prefix_nodes.txt, the node coordinates.
• sample_prefix_values.txt, the data values;

• fem_prefix_nodes.txt, the node coordinates.
• fem_prefix_elements.txt, the nodes that make up each element;
• fem_prefix_values.txt, created by the program, and contains the projections of the data values onto the finite element space, that is, these may be regarded as coefficients of finite element functions representing the projections of the data.

Licensing:

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

Languages:

FEM1D_PROJECT 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:

FEM1D, a data directory which contains examples of 1D FEM files, three text files that describe a 1D finite element model;

FEM1D, a FORTRAN77 program which applies the finite element method to a 1D linear two point boundary value problem.

FEM1D_ADAPTIVE, a FORTRAN77 program which applies the finite element method to a 1D linear two point boundary value problem using adaptive refinement to improve the solution.

FEM1D_BVP_LINEAR, a FORTRAN77 program which applies the finite element method, with piecewise linear elements, to a two point boundary value problem in one spatial dimension.

FEM1D_NONLINEAR, a FORTRAN77 program which applies the finite element method to a 1D nonlinear two point boundary value problem.

FEM1D_PMETHOD, a FORTRAN77 program which applies the p-method version of the finite element method to a 1D linear two point boundary value problem.

FEM1D_SAMPLE, a FORTRAN77 program which samples a scalar or vector finite element function of one variable, defined by FEM files, returning interpolated values at the sample points.

FEM2D_PROJECT, a FORTRAN90 program which projects a function F(X,Y) into a given finite element space of piecewise linear triangular elements.

Reference:

1. Hans Rudolf Schwarz,
   Finite Element Methods,
   Academic Press, 1988,
   ISBN: 0126330107,
   LC: TA347.F5.S3313.
2. Gilbert Strang, George Fix,
   An Analysis of the Finite Element Method,
   Cambridge, 1973,
   ISBN: 096140888X,
   LC: TA335.S77.
3. Olgierd Zienkiewicz,
   The Finite Element Method,
   Sixth Edition,
   Butterworth-Heinemann, 2005,
   ISBN: 0750663200,
   LC: TA640.2.Z54.

Source Code:

• fem1d_project.f, the source code.
• fem1d_project.sh, commands to compile the source code.

Examples and Tests:

POWERS starts with sample data for the vector function f(x)=[ 1, x, x^2], on a grid of 11 equally spaced nodes from 0 to 10, and projects this onto a piecewise linear grid of 6 equally spaced nodes from 0 to 10.

• sample_powers_nodes.txt, the sample nodes.
• sample_powers_values.txt, the sample nodal values.
• fem_powers_nodes.txt, the FEM nodes.
• fem_powers_elements.txt, the FEM elements.
• fem_powers_values.txt, the projected FEM nodal values.

List of Routines:

• MAIN is the main program for FEM1D_PROJECT.
• CH_CAP capitalizes a single character.
• CH_EQI is a case insensitive comparison of two characters for equality.
• CH_TO_DIGIT returns the integer value of a base 10 digit.
• DTABLE_DATA_READ reads data from a DTABLE file.
• DTABLE_DATA_WRITE writes DTABLE data to a file.
• DTABLE_HEADER_READ reads the header from a DTABLE file.
• DTABLE_HEADER_WRITE writes the header to a DTABLE file.
• DTABLE_WRITE writes a DTABLE to a file.
• FEM1D_APPROXIMATE approximates data at sample points with an FEM function.
• FILE_COLUMN_COUNT counts the number of columns in the first line of a file.
• FILE_ROW_COUNT counts the number of row records in a file.
• GET_UNIT returns a free FORTRAN unit number.
• ITABLE_DATA_READ reads data from an ITABLE file.
• ITABLE_HEADER_READ reads the header from an integer table file.
• PIECEWISE_LINEAR_PRODUCT_INTEGRAL: piecewise linear product integral.
• R83_NP_FS factors and solves a R83 system.
• R8VEC_BRACKET3 finds the interval containing or nearest a given value.
• S_BLANK_DELETE removes blanks from a string, left justifying the remainder.
• S_TO_I4 reads an I4 from a string.
• S_TO_I4VEC reads an I4VEC from a string.
• S_TO_R8 reads an R8 from a string.
• S_TO_R8VEC reads an R8VEC from a string.
• S_WORD_COUNT counts the number of "words" in a string.
• TIMESTAMP prints the current YMDHMS date as a time stamp.
• TIMESTRING writes the current YMDHMS date into a string.

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