libmatheval library.
Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2011, 2012 Aleksandar Samardzic
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being “Rationale and history”, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “Copying”.
libmatheval manualGNU libmatheval is small library of procedures for evaluating
mathematical functions. This manual documents how to use the library;
this is manual edition 1.1.9, last updated 22 September 2012,
corresponding to library version 1.1.9.
GNU libmatheval is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
GNU libmatheval is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with GNU libmatheval. If not, see <http://www.gnu.org/licenses/>.
GNU libmatheval is library comprising several procedures that
makes possible to create in-memory tree representation of mathematical
functions over single or multiple variables and later use this
representation to evaluate function for specified variable values, to
create corresponding tree for function derivative over specified
variable or to get back textual representation of in-memory tree.
This section discuss use of programming interface exposed by library from C programs. Readers interested in Fortran interface should switch immediately to Fortran interface section.
In order to use GNU libmatheval library from C code, it is
necessary first to include header file matheval.h from all
files calling GNU libmatheval procedures and then refer to
libmatheval library among other linker option. Thus, command
to compile C program using library and stored in file example.c
using GNU C compiler would look like (supposing that library is
installed using default prefix /usr/local/lib):
gcc example.c -I/usr/local/include -L/usr/local/lib -lmatheval -o example
Alternatively, pkg-config metadata file for libmatheval
is installed along with the library too, thus on system with
pkg-config installed following command could be used instead:
gcc example.c $(pkg-config --cflags --libs) -o example
First step in actually utilizing library after including appropriate
header file would be to declare variable of void * type to
point to evaluator object that will represent given mathematical
function:
void *f;
Then, given that textual representation of function is stored into
string buffer, evaluator object corresponding to given
mathematical function could be created using evaluator_create
procedure (see evaluator_create) as follows (see documentation
for this procedure also for description of notation that should be
used to describe mathematical functions):
f = evaluator_create (buffer);
assert (f);
Return value should be always checked, because above procedure will
return null pointer if there exist syntax errors in notation. After
that, one could utilize evaluator_get_variables (see
evaluator_get_variables) procedure to obtain a list of variable
names appearing in function:
{
char **names;
int count;
int i;
evaluator_get_variables (f, &names, &count);
for (i = 0; i < count; i++)
printf ("%s ", names[i]);
printf ("\n");
}
Procedure evaluator_evaluate (see evaluator_evaluate)
could be used to evaluate function for specific variable values. Say
that above function is over variable “x” only, then following code
will evaluate and print function value for x = 0.1:
{
char *names[] = { "x" };
double values[] = { 0.1 };
printf ("f(0.1) = %g\n", evaluator_evaluate (f, 1, names,
values));
}
Or alternatively, since function is over variable with standard name
“x”, convenience procedure evaluator_evaluate_x
(evaluator_evaluate_x) could be used to accomplish same by
following:
printf ("f(0.1) = %g\n", evaluator_evaluate_x (f, 0.1));
Evaluator object for function derivative over some variable could be created from evaluator object for given function. In order to accomplish this, a declaration for derivative evaluator object should be added to variable declarations section:
void *f_prim;
After that (supposing that “x” is used as derivation variable),
derivative evaluator object could be created using
evaluator_derivative procedure (see
evaluator_derivative):
f_prim = evaluator_derivative (f, "x");
or alternatively using evaluator_derivative_x convenience
procedure (see evaluator_derivative_x):
f_prim = evaluator_derivative_x (f);
Derivative evaluator object could be used to evaluate derivative
values or say textual representation of derivative could be written to
standard output through utilizing evaluator_get_string
procedure (see evaluator_get_string) to get string representing
given evaluator. Following code would accomplish this:
printf (" f'(x) = %s\n", evaluator_get_string (f_prim));
All evaluator objects must be destroyed after finished with using them
and evaluator_destroy procedure (see evaluator_destroy)
is intended for this:
evaluator_destroy (f);
evaluator_destroy (f_prim);
Here follows complete program connecting above fragments. Program read from standard input string representing function over variable “x”, create evaluators for function and its first derivative, print textual representation of function derivative to standard output, then read value of variable “x” and finally print to standard output values of function and its first derivative for given value of variable “x”.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <matheval.h>
/* Size of input buffer. */
#define BUFFER_SIZE 256
/* Program is demonstrating use of GNU libmatheval library of procedures
for evaluating mathematical functions. */
int
main (int argc, char **argv)
{
char buffer[BUFFER_SIZE]; /* Input buffer. */
int length; /* Length of above buffer. */
void *f, *f_prim; /* Evaluators for function and function derivative. */
char **names; /* Function variables names. */
int count; /* Number of function variables. */
double x; /* Variable x value. */
int i; /* Loop counter. */
/* Read function. Function has to be over variable x, or result may
be undetermined. Size of textual represenatation of function is
bounded here to 256 characters, in real conditions one should
probably use GNU readline() instead of fgets() to overcome this
limit. */
printf ("f(x) = ");
fgets (buffer, BUFFER_SIZE, stdin);
length = strlen (buffer);
if (length > 0 && buffer[length - 1] == '\n')
buffer[length - 1] = '\0';
/* Create evaluator for function. */
f = evaluator_create (buffer);
assert (f);
/* Print variable names appearing in function. */
evaluator_get_variables (f, &names, &count);
printf (" ");
for (i = 0; i < count; i++)
printf ("%s ", names[i]);
printf ("\n");
/* Create evaluator for function derivative and print textual
representation of derivative. */
f_prim = evaluator_derivative_x (f);
printf (" f'(x) = %s\n", evaluator_get_string (f_prim));
/* Read variable x value. */
printf ("x = ");
scanf ("%lf", &x);
/* Calculate and print values of function and its derivative for given
value of x. */
printf (" f(%g) = %g\n", x, evaluator_evaluate_x (f, x));
printf (" f'(%g) = %g\n", x, evaluator_evaluate_x (f_prim, x));
/* Destroy evaluators. */
evaluator_destroy (f);
evaluator_destroy (f_prim);
exit (EXIT_SUCCESS);
}
Above example exercise most of library main procedures (see Main entry points), as well as some of convenience procedures (see Convenience procedures). For full documentation, see Reference.
This section documents procedures constituting GNU libmatheval
library. The convention is that all procedures have evaluator_
prefix.
evaluator_create #include <matheval.h>
void *evaluator_create (char *string);
Create evaluator object from string containing mathematical
representation of function. Evaluator object could be used later to
evaluate function for specific variable values or to calculate
function derivative over some variable.
String representation of function is allowed to consist of decimal numbers, constants, variables, elementary functions, unary and binary operations.
Supported constants are (names that should be used are given in
parenthesis): e (e), log2(e) (log2e), log10(e)
(log10e), ln(2) (ln2), ln(10) (ln10), pi
(pi), pi / 2 (pi_2), pi / 4 (pi_4), 1 / pi
(1_pi), 2 / pi (2_pi), 2 / sqrt(pi) (2_sqrtpi),
sqrt(2) (sqrt) and sqrt(1 / 2) (sqrt1_2).
Variable name is any combination of alphanumericals and _
characters beginning with a non-digit that is not elementary function
name.
Supported elementary functions are (names that should be used are given
in parenthesis): exponential (exp), logarithmic (log),
square root (sqrt), sine (sin), cosine (cos),
tangent (tan), cotangent (cot), secant (sec),
cosecant (csc), inverse sine (asin), inverse cosine
(acos), inverse tangent (atan), inverse cotangent
(acot), inverse secant (asec), inverse cosecant
(acsc), hyperbolic sine (sinh), cosine (cosh),
hyperbolic tangent (tanh), hyperbolic cotangent (coth),
hyperbolic secant (sech), hyperbolic cosecant (csch),
hyperbolic inverse sine (asinh), hyperbolic inverse cosine
(acosh), hyperbolic inverse tangent (atanh), hyperbolic
inverse cotangent (acoth), hyperbolic inverse secant
(asech), hyperbolic inverse cosecant (acsch), absolute
value (abs), Heaviside step function (step) with value 1
defined for x = 0, Dirac delta function with infinity (delta) and
not-a-number (nandelta) values defined for x = 0, and error
function (erf).
Supported unary operation is unary minus ('-').
Supported binary operations are addition ('+'), subtraction
('+'), multiplication ('*'), division multiplication
('/') and exponentiation ('^').
Usual mathematical rules regarding operation precedence
apply. Parenthesis ('(' and ')') could be used to change
priority order.
Blanks and tab characters are allowed in string representing function; newline characters must not appear in this string.
Pointer to evaluator object if operation successful, null pointer otherwise. Evaluator object is opaque, one should only use return pointer to pass it to other functions from library.
evaluator_destroy, evaluator_evaluate, evaluator_get_string, evaluator_get_variables, evaluator_derivative
evaluator_destroy #include <matheval.h>
void evaluator_destroy (void *evaluator);
Destroy evaluator object pointer by evaluator pointer. After
returning from this call evaluator pointer must not be
dereferenced because evaluator object gets invalidated.
None.
evaluator_evaluate #include <matheval.h>
double evaluator_evaluate (void *evaluator, int count, char **names,
double *values);
Calculate value of function represented by evaluator object for given
variable values. Evaluator object is pointed by evaluator
pointer. Variable names and corresponding values are given by
names and values array respectively. Length of arrays
is given by count argument.
Function value for given variable values. If some variable that appears in function is not mentioned in arguments, result is indeterminate. If all variables that appear in function are given, presence of variable or variables that doesn't appear in function in arguments has no effect, i.e. result is still exact.
evaluator_create, evaluator_destroy, evaluator_evaluate_x, evaluator_evaluate_x_y, evaluator_evaluate_x_y_z
evaluator_get_string #include <matheval.h>
char *evaluator_get_string (void *evaluator);
Return textual representation (i.e. mathematical function) of
evaluator object pointed by evaluator. For notation used, see
evaluator_create documentation.
String with textual representation of evaluator object. This string is stored in evaluator object and caller must not free pointer returned by this function. Returned string is valid until evaluator object destroyed.
evaluator_create, evaluator_destroy, evaluator_get_variables
evaluator_get_variables #include <matheval.h>
void evaluator_get_variables (void *evaluator, char ***names, int *count);
Return array of strings with names of variables appearing in function represented by evaluator. Address of array first element is stored by function in location pointed by second argument and number of array elements is stored in location pointed by third argument. Array with function variable names is stored in evaluator object and caller must not free any of strings returned by this function nor array itself. Returned values are valid until evaluator object destroyed.
None.
evaluator_create, evaluator_destroy, evaluator_get_string
evaluator_derivative #include <matheval.h>
void *evaluator_derivative (void *evaluator, char *name);
Create evaluator for derivative of function represented by given
evaluator object. Evaluator object is pointed to by evaluator
pointer and derivation variable is determined by name argument.
Calculated derivative is in mathematical sense correct no matters of
fact that derivation variable appears or not in function represented
by evaluator.
Pointer to evaluator object representing derivative of given function.
evaluator_create, evaluator_destroy, evaluator_derivative_x, evaluator_derivative_y, evaluator_derivative_z
evaluator_evaluate_x #include <matheval.h>
double evaluator_evaluate_x (void *evaluator, double x);
Convenience function to evaluate function for given variable “x” value. Function is equivalent to following:
char *names[] = { "x" };
double values[] = { x };
evaluator_evaluate (evaluator, sizeof (names) / sizeof(names[0]),
names, values);
See evaluator_evaluate for further information.
Value of function for given value of variable “x”.
evaluator_create, evaluator_destroy, evaluator_evaluate
evaluator_evaluate_x_y #include <matheval.h>
double evaluator_evaluate_x_y (void *evaluator, double x, double y);
Convenience function to evaluate function for given variables “x” and “y” values. Function is equivalent to following:
char *names[] = { "x", "y" };
double values[] = { x, y };
evaluator_evaluate (evaluator, sizeof (names) / sizeof(names[0]),
names, values);
See evaluator_evaluate for further information.
Value of function for given values of variables “x” and “y”.
evaluator_create, evaluator_destroy, evaluator_evaluate
evaluator_evaluate_x_y_z #include <matheval.h>
double evaluator_evaluate_x_y_z (void *evaluator, double x, double y,
double z);
Convenience function to evaluate function for given variables “x”, “y” and “z” values. Function is equivalent to following:
char *names[] = { "x", "y", "z" };
double values[] = { x, y, z };
evaluator_evaluate (evaluator, sizeof (names) / sizeof(names[0]),
names, values);
See evaluator_evaluate for further information.
Value of function for given values of variables “x”, “y” and “z”.
evaluator_create, evaluator_destroy, evaluator_evaluate
evaluator_derivative_x #include <matheval.h>
void *evaluator_derivative_x (void *evaluator);
Convenience function to differentiate function using “x” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, "x");
See evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “x”.
evaluator_create, evaluator_destroy, evaluator_derivative
evaluator_derivative_y #include <matheval.h>
void *evaluator_derivative_y (void *evaluator);
Convenience function to differentiate function using “y” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, "y");
See evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “y”.
evaluator_create, evaluator_destroy, evaluator_derivative
evaluator_derivative_z #include <matheval.h>
void *evaluator_derivative_z (void *evaluator);
Convenience function to differentiate function using “z” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, "z");
See evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “z”.
evaluator_create, evaluator_destroy, evaluator_derivative
Fortran interface to GNU libmatheval library is very similar to
C interface; still, complete documentation from Reference is
reproduced here using Fortran terms in order to have Fortran
programmer not to mess with C terms that he may not understand.
Besides documentation for all library exported procedures, an example
Fortran program of structure similar to sequence of code fragments
presented for C programmers in Introduction section as well as
notes on how to link library with Fortran programs are presented here.
Since passing arguments between C and Fortran is not (yet) standardized, Fortran interface of library applies only to GNU Fortran 77 compiler; but note that same interface is working fine for GNU Fortran 95 compiler. Requests to adapt interface to other Fortran compilers are welcome (see section Bugs for contact information), under condition that access to corresponding compiler is provided.
evaluator_create integer*8 function evaluator_create (string) character(len=*) ::
string end function evaluator_create
Create evaluator object from string containing mathematical
representation of function. Evaluator object could be used later to
evaluate function for specific variable values or to calculate
function derivative over some variable.
String representation of function is allowed to consist of decimal numbers, constants, variables, elementary functions, unary and binary operations.
Supported constants are (names that should be used are given in
parenthesis): e (e), log2(e) (log2e), log10(e)
(log10e), ln(2) (ln2), ln(10) (ln10), pi
(pi), pi / 2 (pi_2), pi / 4 (pi_4), 1 / pi
(1_pi), 2 / pi (2_pi), 2 / sqrt(pi) (2_sqrtpi),
sqrt(2) (sqrt) and sqrt(1 / 2) (sqrt1_2).
Variable name is any combination of alphanumericals and _
characters beginning with a non-digit that is not elementary function
name.
Supported elementary functions are (names that should be used are given
in parenthesis): exponential (exp), logarithmic (log),
square root (sqrt), sine (sin), cosine (cos),
tangent (tan), cotangent (cot), secant (sec),
cosecant (csc), inverse sine (asin), inverse cosine
(acos), inverse tangent (atan), inverse cotangent
(acot), inverse secant (asec), inverse cosecant
(acsc), hyperbolic sine (sinh), cosine (cosh),
hyperbolic tangent (tanh), hyperbolic cotangent (coth),
hyperbolic secant (sech), hyperbolic cosecant (csch),
hyperbolic inverse sine (asinh), hyperbolic inverse cosine
(acosh), hyperbolic inverse tangent (atanh), hyperbolic
inverse cotangent (acoth), hyperbolic inverse secant
(asech), hyperbolic inverse cosecant (acsch), absolute
value (abs), Heaviside step function (step) with value 1
defined for x = 0, Dirac delta function with infinity (delta) and
not-a-number (nandelta) values defined for x = 0, and error
function (erf)
Supported unary operation is unary minus ('-').
Supported binary operations are addition ('+'), subtraction
('+'), multiplication ('*'), division multiplication
('/') and exponentiation ('^').
Usual mathematical rules regarding operation precedence
apply. Parenthesis ('(' and ')') could be used to change
priority order.
Blanks and tab characters are allowed in string representing function; newline characters must not appear in this string.
Positive 64-bit integer representing evaluator object unique handle if operation successful, 0 otherwise. Return value should be used only to pass it to other functions from library.
Fortran evaluator_destroy, Fortran evaluator_evaluate, Fortran evaluator_get_string_length, Fortran evaluator_get_string_chars, Fortran evaluator_get_variables_length, Fortran evaluator_get_variables_chars, Fortran evaluator_derivative
evaluator_destroy subroutine evaluator_destroy (evaluator) integer*8 :: evaluator end
subroutine evaluator_destroy
Destroy evaluator object denoted by evaluator handle. After
returning from this call evaluator object gets invalidated, so value
of evaluator handle should not be used any more.
None.
evaluator_evaluate double precision function evaluator_evaluate (evaluator, count, names,
values) integer*8 :: evaluator integer :: count character(len=*) ::
names double precision :: values dimension values(*) end function
evaluator_evaluate
Calculate value of function represented by evaluator object for given
variable values. Evaluator object is identified by evaluator
handle. Variable names are given by names string and
corresponding values are given by values array respectively.
Number of variables is given by count argument. Variable names
in names string should be delimited by one or more blank
characters.
Function value for given variable values. If some variable that appears in function is not mentioned in arguments, result is indeterminate. If all variables that appear in function are given, presence of variable or variables that doesn't appear in function in arguments has no effect, i.e. result is still exact.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_evaluate_x, Fortran evaluator_evaluate_x_y, Fortran evaluator_evaluate_x_y_z
evaluator_get_string_length integer function evaluator_get_string_length (evaluator) integer*8 ::
evaluator end function evaluator_get_string_length
Return length of textual representation (i.e. mathematical function)
of evaluator object pointed by evaluator.
Evaluator textual representation string length.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_get_string_chars
evaluator_get_string_chars subroutine evaluator_get_string_chars (evaluator) integer*8 ::
evaluator character(len=*) :: string end subroutine
evaluator_get_string_chars
Write textual representation (i.e. mathematical function) of evaluator
object pointed by evaluator to string specified. For notation
used, see Fortran evaluator_create documentation. In order to
declare string of appropriate length to be passed to this function,
Fortran evaluator_get_string_length function should be utilized.
None.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_get_string_length
evaluator_get_variables_length integer function evaluator_get_variables_length (evaluator) integer*8
:: evaluator end function evaluator_get_variables_length
Return length of string with names of all variables (separated by a
blank character) appearing in evaluator object pointed by
evaluator.
Variable names string length.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_get_variables_chars
evaluator_get_variables_chars subroutine evaluator_get_variables_chars (evaluator) integer*8 ::
evaluator character(len=*) :: string end subroutine
evaluator_get_variables_chars
Write names of all variables appearing in evaluator object pointed by
evaluator into given string (separated by a blank character).
In order to declare string of appropriate length to be passed to this
function, Fortran evaluator_get_variables_length function should
be utilized.
None.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_get_variables_length
evaluator_derivative integer*8 function evaluator_derivative (evaluator, name) integer*8 ::
evaluator character(len=*) :: name end function evaluator_derivative
Create evaluator for derivative of function represented by given
evaluator object. Evaluator object is identified by evaluator
handle and derivation variable is determined by name argument.
Calculated derivative is in mathematical sense correct no matters of
fact that derivation variable appears or not in function represented
by evaluator.
64-bit integer uniquely identifying evaluator object representing derivative of given function.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_derivative_x, Fortran evaluator_derivative_y, Fortran evaluator_derivative_z
evaluator_evaluate_x double precision function evaluator_evaluate_x (evaluator, x)
integer*8 :: evaluator double precision :: x end function
evaluator_evaluate_x
Convenience function to evaluate function for given variable “x” value. Function is equivalent to following:
evaluator_evaluate (evaluator, 1, 'x', (/ x /))
See Fortran evaluator_evaluate for further information.
Value of function for given value of variable “x”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_evaluate
evaluator_evaluate_x_y double precision function evaluator_evaluate_x_y (evaluator, x, y)
integer*8 :: evaluator double precision :: x, y end function
evaluator_evaluate_x_y
Convenience function to evaluate function for given variables “x” and “y” values. Function is equivalent to following:
evaluator_evaluate (evaluator, 2, 'x y', (/ x, y /))
See Fortran evaluator_evaluate for further information.
Value of function for given values of variables “x” and “y”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_evaluate
evaluator_evaluate_x_y_z double precision function evaluator_evaluate_x_y_z (evaluator, x, y,
z) integer*8 :: evaluator double precision :: x, y, z end function
evaluator_evaluate_x_y_z
Convenience function to evaluate function for given variables “x”, “y” and “z” values. Function is equivalent to following:
evaluator_evaluate (evaluator, 2, 'x y z', (/ x, y, z /))
See Fortran evaluator_evaluate for further information.
Value of function for given values of variables “x”, “y” and “z”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_evaluate
evaluator_derivative_x integer*8 function evaluator_derivative_x (evaluator) integer*8 ::
evaluator end function evaluator_derivative_x
Convenience function to differentiate function using “x” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, 'x');
See Fortran evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “x”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_derivative
evaluator_derivative_y integer*8 function evaluator_derivative_y (evaluator) integer*8 ::
evaluator end function evaluator_derivative_y
Convenience function to differentiate function using “y” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, 'y');
See Fortran evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “y”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_derivative
evaluator_derivative_z integer*8 function evaluator_derivative_z (evaluator) integer*8 ::
evaluator end function evaluator_derivative_z
Convenience function to differentiate function using “z” as derivation variable. Function is equivalent to:
evaluator_derivative (evaluator, 'z');
See Fortran evaluator_derivative for further information.
Evaluator object representing derivative of function over variable “z”.
Fortran evaluator_create, Fortran evaluator_destroy, Fortran evaluator_derivative
Here follows sample program demonstrating use of library Fortran interface. Hopefully, comments throughout code will be enough for Fortran programmer to get acquainted with library usage. Basic functioning of program is equivalent to code presented for C programmer in Introduction sequence, except that textual representation of function derivative is not printed to standard output and this is avoided simply because of Fortran 77 ugly string handling. Following code is written in Fortran 77 with GNU Fortran 77 compiler extensions (most notable of these certainly is free form of source code).
! Program is demonstrating use of GNU libmatheval library of procedures
! for evaluating mathematical functions.
program evaluator
implicit none
! Declarations of GNU libmatheval procedures used.
integer*8 evaluator_create
integer*8 evaluator_derivative_x
double precision evaluator_evaluate_x
external evaluator_destroy
! Size of input buffer.
integer :: BUFFER_SIZE
parameter(BUFFER_SIZE = 256)
character(len = BUFFER_SIZE) :: buffer ! Input buffer.
integer*8 :: f, f_prim ! Evaluators for function and function derivative.
double precision :: x ! Variable x value.
! Read function. Function has to be over variable x, or result may
! be undetermined. Size of textual represenatation will be truncated
! here to BUFFER_SIZE characters, in real conditions one should
! probably come with something smarter to avoid this limit.
write (*, '(A)') 'f(x) = '
read (*, '(A)') buffer
! Create evaluator for function.
f = evaluator_create (buffer);
if (f == 0) stop
! Create evaluator for function derivative.
f_prim = evaluator_derivative_x (f);
if (f_prim == 0) stop
! Read variable x value.
write (*, '(A)') 'x = '
read (*, *) x
! Calculate and print values of function and its derivative for given
! value of x.
write (*,*) ' f (', x, ') = ', evaluator_evaluate_x (f, x)
write (*,*) ' f'' (', x, ') = ', evaluator_evaluate_x (f_prim, x)
! Destroy evaluators.
call evaluator_destroy (f)
call evaluator_destroy (f_prim)
end program evaluator
In order to be able to reference GNU libmatheval procedures
from Fortran code, declarations of procedures that will be used should
be repeated, like demonstrated by Fortran sample program (once
when interface upgraded to Fortran 90, modules and use
statement will be employed here). Command for compilation Fortran
program using library and stored in file example.f using GNU
Fortran 77 compiler would look like (again supposing that library is
installed using default prefix /usr/local/lib):
f77 example.f -ff90 -ffree-form -L/usr/local/lib -lmatheval -o example
As usual with a free software project, ultimate reference for anyone
willing to hack on it is its source code. Every effort is put to have
source code properly commented; having in mind that GNU
libmatheval is rather simple project, it is reasonable to
expect that this would be enough for anyone interested in project
internals to get acquainted with it. Still, this section will briefly
explain project design. See Project structure section for
description of where each functionality is located in source code.
Mathematical functions are represented as trees in computer memory. There are five different nodes in such a tree: number, constants, variables, functions, unary operations and binary operations. Single data structure is employed for tree nodes, while union is used over what is different among them. Numbers have unique value, unary and binary operations have unique pointer(s) to their operand(s) node(s). To represent constants, variables and functions, a symbol table is employed; thus constants, variables and functions have unique pointers to corresponding symbol table records (functions also have unique pointer to their argument node). All operations related to functions (e.g. evaluation or derivative calculation) are implemented as recursive operations on tree nodes. There exist a node operation that is not visible as external procedure and this is node simplification; this operation is very important regarding overall efficiency of other operations and is employed each time when new tree created.
Symbol table is implemented as hash table, where each bucket has linked list of records stored in it. Records store information of symbol name and type (variable or function), as well as some unique information related to evaluation: variable records store temporary variable value and function records store pointer to procedure used to actually calculate function value during evaluation. Hashing function described in A.V. Aho, R. Sethi, J.D. Ullman, “Compilers - Principle, Techniques, and Tools”, Addison-Wesley, 1986, pp 435-437 is used. Symbol tables are reference counted objects, i.e. could be shared.
Evaluator objects actually consists of function tree and reference to symbol table. Most of operations on evaluator objects are simply delegated to function tree root node.
For parsing strings representing mathematical functions, Lex and Yacc are employed. Scanner is creating symbol table records for variables, while for constants and functions it is only looking up existing symbol table records (before starting scanning, symbol table should be populated with records for constants and functions recognized by scanner). Parser is responsible for building function tree representation.
Couple error reporting procedures, as well as replacements for standard memory allocation routines are also present. These are rather standard for all GNU projects, so deserve no further discussion. Further present in project are couple procedures for mathematical functions not implemented by C standard library, like cotangent, inverse cotangent and some hyperbolic and inverse hyperbolic functions.
Also present in project are stubs for Fortran code calling library. These stubs uses knowledge of GNU Fortran 77 compiler calling conventions, take parameters from Fortran 77 calls, eventually mangle them to satisfy primary C library interface and call library procedures to actually do the work, finally eventually mangling return values to satisfy Fortran 77 calling conventions again.
Most important thing to know before criticizing library design is that it is intentionally left as simple as it could be. Decision is now that eventual library usage should direct its improvements. Some obvious and intended improvements if enough interest for library arise are enumerated in Intended improvements section. If having further suggestions, pleas see Bugs sections for contact information.
Interesting source files are mostly concentrated in lib subdirectory of distribution. Basic arrangement is rather standard for GNU projects, thus scanner is in scanner.l file, parser in parser.y, error handling routines are in error.c and error.h files, replacements for standard memory allocation routines are in xmalloc.c and xmalloc.h, additional mathematical functions are in xmath.c and xmath.c. Project specific files are: node.h and node.c files for tree representing mathematical function data structures and procedures, symbol_table.c and symbol_table.h for symbol table data structures and procedures and finally evaluator.c and matheval.h for evaluator object data structures and procedures (evaluator object data structure is moved to .c file because matheval.h is public header file and this data structure should be opaque). Fortran interface is implemented in f77_interface.c file.
File libmatheval.texi under doc subdirectory of distribution contains Texinfo source of project documentation (i.e. what you are reading now).
Subdirectory tests contains library test suite. Kind of mixed
design is employed here - GNU autotest is used for test framework in
order to achieve more portability, while number of small Guile scripts
are performing tests. File matheval.c in tests
subdirectory contains program extending Guile interpreter with GNU
libmatheval procedures. Files with .at extension in
same subdirectory in turn consist of fragments of Guile code that this
extended Guile interpreter executes in order to conduct tests. File
matheval.sh is shell wrapper for program contained in
matheval.c file; this wrapper is used by autotest during
testing instead of original program. Most interesting aspect of code
from tests subdirectory is certainly Guile interface for
library that is implemented in matheval.c file; anyone
intending to write more tests must before approaching this task become
familiar with this interface.
As stated in Design notes section, GNU libmatheval is
designed with intention to be simple and understandable and to
eventually have its usage to govern improvements. Thus, further work
will be primarily directed by user requests and of course, as usual
with free software projects, with amount of spare time of primary
developer (see Bugs for contact information). However, there
exist several obvious improvements that I'm willing to work on
immediately if any interest of library arise and these are (in random
order) listed below:
asserts
left in code that may be replaced with some other mechanism, also
probably error handling of more error conditions should be added to
library.
There exists also an improvement that is obvious and necessary but because I'm not native speaker I'm unfortunately not able to accomplish it anything more than I already tried:
If you encounter something that you think is a bug, please report it immediately. Try to include a clear description of the undesired behavior. A test case that exhibits the bug or maybe even patch fixing it, would too be of course very useful.
Suggestions on improving library would be also more than welcome. Please see Hacking, for further information.
Please direct bug reports and eventual patches to
[email protected] mailing list. For suggestions
regarding improvements and other libmatheval related
conversation use author e-mail address
[email protected].
The library is developed as a back-end for “Numerical Analysis” course taught during 1999/2000, 2000/2001 and 2001/2002 school years at Department of Mathematics, University of Belgrade. Most numerical libraries (library accompanying “Numerical Recipes” book most notably example) are asking programmer to write corresponding C code when it comes to evaluate mathematical functions. It seemed to me that it would be more appropriate (well, at least for above mentioned course) to have library that will make possible to specify functions as strings and then have them evaluated for given variable values, so I wrote first version of library during November 1999. Fortran interface is added to the library later; during January 2001 interface for Pacific Sierra VAST Fortran 90 translator was implemented and during September 2001 it was replaced by interface for Intel Fortran 90 compiler 1. This library eventually went into rather stable state and was tested by number of other programs implementing various numerical methods and developed for the same course.
After completing engagement with this course, I thought it may be interesting for someone else to use this code and decided to make it publicly available. So, having some spare time during June 2002, I re-wrote whole library in preparation for public release, now employing simpler overall design and also using GNU auto-tools and what else was necessary according to GNU guidelines. The benefit is that final product looks much better now (well, at least to me and at least at the very moment of this writing), the drawback is that code is not thoroughly tested again. But certainly author would be more than happy to further improve and maintain it. Please see Bugs, for contact information.
The library source code was hosted on Savannah (http://savannah.gnu.org/) since Septembar 2002. In September 2003, library officially became part of GNU project.
Version 1.1, March 2000
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evaluator_create: evaluator_createevaluator_derivative: evaluator_derivativeevaluator_derivative_x: evaluator_derivative_xevaluator_derivative_y: evaluator_derivative_yevaluator_derivative_z: evaluator_derivative_zevaluator_destroy: evaluator_destroyevaluator_evaluate: evaluator_evaluateevaluator_evaluate_x: evaluator_evaluate_xevaluator_evaluate_x_y: evaluator_evaluate_x_yevaluator_evaluate_x_y_z: evaluator_evaluate_x_y_zevaluator_get_string: evaluator_get_stringevaluator_get_variables: evaluator_get_variablesFortran, evaluator_create: Fortran evaluator_createFortran, evaluator_derivative: Fortran evaluator_derivativeFortran, evaluator_derivative_x: Fortran evaluator_derivative_xFortran, evaluator_derivative_y: Fortran evaluator_derivative_yFortran, evaluator_derivative_z: Fortran evaluator_derivative_zFortran, evaluator_destroy: Fortran evaluator_destroyFortran, evaluator_evaluate: Fortran evaluator_evaluateFortran, evaluator_evaluate_x: Fortran evaluator_evaluate_xFortran, evaluator_evaluate_x_y: Fortran evaluator_evaluate_x_yFortran, evaluator_evaluate_x_y_z: Fortran evaluator_evaluate_x_y_zFortran, evaluator_get_string_chars: Fortran evaluator_get_string_charsFortran, evaluator_get_string_length: Fortran evaluator_get_string_lengthFortran, evaluator_get_variables_chars: Fortran evaluator_get_variables_charsFortran, evaluator_get_variables_length: Fortran evaluator_get_variables_lengthlibmatheval manual
[1] That was in turn replaced by interface for GNU Fortran 77 compiler in order to meet requirement that no GNU project should require use of non-free software