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Math::Algebra::Symbols
Symbolic Algebra in Pure Perl.

Math::Algebra::Symbols - Symbolic Algebra in Pure Perl.


DESCRIPTION




This package supplies a set of functions and operators to manipulate

operator expressions algebraically using the familiar Perl syntax.

These expressions are constructed from Symbols, Operators, and Functions, and processed via Methods. For examples, see: Examples.




=head2 Symbols



Symbols are created with the exported B<symbols()> constructor routine:

Example t/constants.t


 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: constants.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>1;

 

 my ($x, $y, $i, $o, $pi) = symbols(qw(x y i 1 pi));

 

 ok( "$x $y $i $o $pi"   eq   '$x $y i 1 $pi'  );



The B<symbols()> routine constructs references to symbolic variables and

symbolic constants from a list of names and integer constants.

The special symbol i is recognized as the square root of -1.

The special symbol pi is recognized as the smallest positive real that satisfies:

Example t/ipi.t


 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: constants.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my ($i, $pi) = symbols(qw(i pi));

 

 ok(  exp($i*$pi)  ==   -1  );

 ok(  exp($i*$pi) <=>  '-1' );

Constructor Routine Name




If you wish to use a different name for the constructor routine, say

B<S>:

Example t/ipi2.t


 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: constants.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols symbols=>'S';

 use Test::Simple tests=>2;

 

 my ($i, $pi) = S(qw(i pi));

 

 ok(  exp($i*$pi)  ==   -1  );

 ok(  exp($i*$pi) <=>  '-1' );

Big Integers




Symbols automatically uses big integers if needed.

Example t/bigInt.t


 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: bigInt.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>1;

 

 my $z = symbols('1234567890987654321/1234567890987654321');

 

 ok( eval $z eq '1');

Operators




L</Symbols> can be combined with L</Operators> to create symbolic expressions:



=head3 Arithmetic operators




=head4 Arithmetic Operators: B<+> B<-> B<*> B</> B<**>

            

Example t/x2y2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplification.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $y) = symbols(qw(x y));

 

 ok(  ($x**2-$y**2)/($x-$y)  ==  $x+$y  );

 ok(  ($x**2-$y**2)/($x-$y)  !=  $x-$y  );

 ok(  ($x**2-$y**2)/($x-$y) <=> '$x+$y' );



The operators: B<+=> B<-=> B<*=> B</=> are overloaded to work

symbolically rather than numerically. If you need numeric results, you

can always B<eval()> the resulting symbolic expression.



=head4 Square root Operator: B<sqrt>



Example t/ix.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: sqrt(-1).

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my ($x, $i) = symbols(qw(x i));

 

 ok(  sqrt(-$x**2)  ==  $i*$x  );

 ok(  sqrt(-$x**2)  <=> 'i*$x' );



The square root is represented by the symbol B<i>, which allows complex

expressions to be processed by Math::Complex.



=head4 Exponential Operator: B<exp>



Example t/expd.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: exp.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my ($x, $i) = symbols(qw(x i));

 

 ok(   exp($x)->d($x)  ==   exp($x)  );

 ok(   exp($x)->d($x) <=>  'exp($x)' );



The exponential operator.



=head4 Logarithm Operator: B<log>



Example t/logExp.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: log: need better example.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>1;

 

 my ($x) = symbols(qw(x));

 

 ok(   log($x) <=>  'log($x)' );



Logarithm to base B<e>.

Note: the above result is only true for x > 0. Symbols does not include domain and range specifications of the functions it uses.




=head4 Sine and Cosine Operators: B<sin> and B<cos>



Example t/sinCos.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplification.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x) = symbols(qw(x));

 

 ok(  sin($x)**2 + cos($x)**2  ==  1  );

 ok(  sin($x)**2 + cos($x)**2  !=  0  );

 ok(  sin($x)**2 + cos($x)**2 <=> '1' );



This famous trigonometric identity is not preprogrammed into B<Symbols>

as it is in commercial products.

Instead: an expression for sin() is constructed using the complex exponential: exp, said expression is algebraically multiplied out to prove the identity. The proof steps involve large intermediate expressions in each step, as yet I have not provided a means to neatly lay out these intermediate steps and thus provide a more compelling demonstration of the ability of Symbols to verify such statements from first principles.




=head3 Relational operators

Relational operators: ==, !=




Example t/x2y2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplification.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $y) = symbols(qw(x y));

 

 ok(  ($x**2-$y**2)/($x-$y)  ==  $x+$y  );

 ok(  ($x**2-$y**2)/($x-$y)  !=  $x-$y  );

 ok(  ($x**2-$y**2)/($x-$y) <=> '$x+$y' );



The relational equality operator B<==> compares two symbolic expressions

and returns TRUE(1) or FALSE(0) accordingly. B<!=> produces the opposite

result.



=head4 Relational operator: B<eq>



Example t/eq.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: solving.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $v, $t) = symbols(qw(x v t));

 

 ok(  ($v eq $x / $t)->solve(qw(x in terms of v t))  ==  $v*$t  );

 ok(  ($v eq $x / $t)->solve(qw(x in terms of v t))  !=  $v+$t  );

 ok(  ($v eq $x / $t)->solve(qw(x in terms of v t)) <=> '$v*$t' );



The relational operator B<eq> is a synonym for the minus B<-> operator,

with the expectation that later on the L<solve()|/Solving equations>

function will be used to simplify and rearrange the equation. You may

prefer to use B<eq> instead of B<-> to enhance readability, there is no

functional difference.



=head3 Complex operators

Complex operators: the dot operator: ^




Example t/dot.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: dot operator.  Note the low priority

 # of the ^ operator.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($a, $b, $i) = symbols(qw(a b i));

 

 ok(  (($a+$i*$b)^($a-$i*$b))  ==  $a**2-$b**2  );

 ok(  (($a+$i*$b)^($a-$i*$b))  !=  $a**2+$b**2  );

 ok(  (($a+$i*$b)^($a-$i*$b)) <=> '$a**2-$b**2' );



Note the use of brackets:  The B<^> operator has low priority.

The ^ operator treats its left hand and right hand arguments as complex numbers, which in turn are regarded as two dimensional vectors to which the vector dot product is applied.




=head4 Complex operators: the B<cross> operator: B<x>



Example t/cross.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: cross operator.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $i) = symbols(qw(x i));

 

 ok(  $i*$x x $x  ==  $x**2  );

 ok(  $i*$x x $x  !=  $x**3  );

 ok(  $i*$x x $x <=> '$x**2' );



The B<x> operator treats its left hand and right hand arguments as

complex numbers, which in turn are regarded as two dimensional vectors

defining the sides of a parallelogram. The B<x> operator returns the

area of this parallelogram.

Note the space before the x, otherwise Perl is unable to disambiguate the expression correctly.




=head4 Complex operators: the B<conjugate> operator: B<~>



Example t/conjugate.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: dot operator.  Note the low priority

 # of the ^ operator.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $y, $i) = symbols(qw(x y i));

 

 ok(  ~($x+$i*$y)  ==  $x-$i*$y  );

 ok(  ~($x-$i*$y)  ==  $x+$i*$y  );

 ok(  (($x+$i*$y)^($x-$i*$y)) <=> '$x**2-$y**2' );



The B<~> operator returns the complex conjugate of its right hand side.



=head4 Complex operators: the B<modulus> operator: B<abs>



Example t/abs.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: dot operator.  Note the low priority

 # of the ^ operator.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my ($x, $i) = symbols(qw(x i));

 

 ok(  abs($x+$i*$x)  ==  sqrt(2*$x**2)  );

 ok(  abs($x+$i*$x)  !=  sqrt(2*$x**3)  );

 ok(  abs($x+$i*$x) <=> 'sqrt(2*$x**2)' );



The B<abs> operator returns the modulus (length) of its right hand side.



=head4 Complex operators: the B<unit> operator: B<!>



Example t/unit.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: unit operator.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>4;

 

 my ($i) = symbols(qw(i));

 

 ok(  !$i      == $i                         );

 ok(  !$i     <=> 'i'                        );

 ok(  !($i+1) <=>  '1/(sqrt(2))+i/(sqrt(2))' );

 ok(  !($i-1) <=> '-1/(sqrt(2))+i/(sqrt(2))' );



The B<!> operator returns a complex number of unit length pointing in

the same direction as its right hand side.



=head3 Equation Manipulation Operators

Equation Manipulation Operators: Simplify operator: +=




Example t/simplify.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplify.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

  

 my ($x) = symbols(qw(x));

 

 ok(  ($x**8 - 1)/($x-1)  ==  $x+$x**2+$x**3+$x**4+$x**5+$x**6+$x**7+1  );      

 ok(  ($x**8 - 1)/($x-1) <=> '$x+$x**2+$x**3+$x**4+$x**5+$x**6+$x**7+1' );



The simplify operator B<+=> is a synonym for the

L<simplify()|/"simplifying_equations:_simplify()"> method, if and only

if, the target on the left hand side initially has a value of undef.

Admittedly this is very strange behavior: it arises due to the shortage of over-rideable operators in Perl: in particular it arises due to the shortage of over-rideable unary operators in Perl. Never-the-less: this operator is useful as can be seen in the Synopsis, and the desired pre-condition can always achieved by using my.




=head4 Equation Manipulation Operators: B<Solve> operator: B<E<gt>>



Example t/solve2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplify.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

  

 my ($t) = symbols(qw(t));

 

 my $rabbit  = 10 + 5 * $t;

 my $fox     = 7 * $t * $t;

 my ($a, $b) = @{($rabbit eq $fox) > $t};

 

 ok( "$a" eq  '1/14*sqrt(305)+5/14'  );      

 ok( "$b" eq '-1/14*sqrt(305)+5/14'  );



The solve operator B<E<gt>> is a synonym for the

L<solve()|/"Solving_equations:_solve()"> method.

The priority of > is higher than that of eq, so the brackets around the equation to be solved are necessary until Perl provides a mechanism for adjusting operator priority (cf. Algol 68).

If the equation is in a single variable, the single variable may be named after the > operator without the use of [...]:


 use Math::Algebra::Symbols;

 my $rabbit  = 10 + 5 * $t;

 my $fox     = 7 * $t * $t;

 my ($a, $b) = @{($rabbit eq $fox) > $t};

 print "$a\n";

 # 1/14*sqrt(305)+5/14

If there are multiple solutions, (as in the case of polynomials), > returns an array of symbolic expressions containing the solutions.

This example was provided by Mike Schilli m@perlmeister.com.




=head2 Functions



Perl operator overloading is very useful for producing compact

representations of algebraic expressions. Unfortunately there are only a

small number of operators that Perl allows to be overloaded. The

following functions are used to provide capabilities not easily expressed

via Perl operator overloading.

These functions may either be called as methods from symbols constructed by the Symbols construction routine, or they may be exported into the user's namespace as described in EXPORT.




=head3 Trigonometric and Hyperbolic functions

Trigonometric functions




Example t/sinCos2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: methods.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>1;

 

 my ($x, $y) = symbols(qw(x y));

 

 ok( (sin($x)**2 == (1-cos(2*$x))/2) );



The trigonometric functions B<cos>, B<sin>, B<tan>, B<sec>, B<csc>,

B<cot> are available, either as exports to the caller's name space, or

as methods.



=head4 Hyperbolic functions



Example t/tanh.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: methods.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols hyper=>1;

 use Test::Simple tests=>1;

 

 my ($x, $y) = symbols(qw(x y));

 

 ok( tanh($x+$y)==(tanh($x)+tanh($y))/(1+tanh($x)*tanh($y)));



The hyperbolic functions B<cosh>, B<sinh>, B<tanh>, B<sech>, B<csch>,

B<coth> are available, either as exports to the caller's name space, or

as methods.



=head3 Complex functions

Complex functions: re and im




 use Math::Algebra::Symbols complex=>1;

Example t/reIm.t


 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: methods.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my ($x, $i) = symbols(qw(x i));

 

 ok( ($i*$x)->re   <=>  0    );

 ok( ($i*$x)->im   <=>  '$x' );



The B<re> and B<im> functions return an expression which represents the

real and imaginary parts of the expression, assuming that symbolic

variables represent real numbers.



=head4 Complex functions: B<dot> and B<cross>



Example t/dotCross.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: methods.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my $i = symbols(qw(i));

 

 ok( ($i+1)->cross($i-1)   <=>  2 );

 ok( ($i+1)->dot  ($i-1)   <=>  0 );



The B<dot> and B<cross> operators are available as functions, either as

exports to the caller's name space, or as methods.



=head4 Complex functions: B<conjugate>, B<modulus> and B<unit>



Example t/conjugate2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: methods.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

 

 my $i = symbols(qw(i));

 

 ok( ($i+1)->unit      <=>  '1/(sqrt(2))+i/(sqrt(2))' );

 ok( ($i+1)->modulus   <=>  'sqrt(2)'                 );

 ok( ($i+1)->conjugate <=>  '1-i'                     );



The B<conjugate>, B<abs> and B<unit> operators are available as

functions: B<conjugate>, B<modulus> and B<unit>, either as exports to

the caller's name space, or as methods. The confusion over the naming of:

the B<abs> operator being the same as the B<modulus> complex function;

arises over the limited set of Perl operator names available for

overloading.

Methods

Methods for manipulating Equations

Simplifying equations: simplify()




Example t/simplify2.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplify.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

  

 my ($x) = symbols(qw(x));

  

 my $y  = (($x**8 - 1)/($x-1))->simplify();  # Simplify method 

 my $z +=  ($x**8 - 1)/($x-1);               # Simplify via +=

 

 ok( "$y" eq '$x+$x**2+$x**3+$x**4+$x**5+$x**6+$x**7+1' );

 ok( "$z" eq '$x+$x**2+$x**3+$x**4+$x**5+$x**6+$x**7+1' );



B<Simplify()> attempts to simplify an expression. There is no general

simplification algorithm: consequently simplifications are carried out

on ad hoc basis. You may not even agree that the proposed simplification

for a given expressions is indeed any simpler than the original. It is

for these reasons that simplification has to be explicitly requested

rather than being performed automagically.

At the moment, simplifications consist of polynomial division: when the expression consists, in essence, of one polynomial divided by another, an attempt is made to perform polynomial division, the result is returned if there is no remainder.

The += operator may be used to simplify and assign an expression to a Perl variable. Perl operator overloading precludes the use of = in this manner.

Substituting into equations: sub()




Example t/sub.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: expression substitution for a variable.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>2;

 

 my ($x, $y) = symbols(qw(x y));

  

 my $e  = 1+$x+$x**2/2+$x**3/6+$x**4/24+$x**5/120;

 

 ok(  $e->sub(x=>$y**2, z=>2)  <=> '$y**2+1/2*$y**4+1/6*$y**6+1/24*$y**8+1/120*$y**10+1'  );

 ok(  $e->sub(x=>1)            <=>  '163/60');



The B<sub()> function example on line B<#1> demonstrates replacing

variables with expressions. The replacement specified for B<z> has no

effect as B<z> is not present in this equation.

Line #2 demonstrates the resulting rational fraction that arises when all the variables have been replaced by constants. This package does not convert fractions to decimal expressions in case there is a loss of accuracy, however:


 my $e2 = $e->sub(x=>1);

 $result = eval "$e2";

or similar will produce approximate results.

At the moment only variables can be replaced by expressions. Mike Schilli, m@perlmeister.com, has proposed that substitutions for expressions should also be allowed, as in:


 $x/$y => $z

Solving equations: solve()




Example t/solve1.t

 #!perl -w

 #______________________________________________________________________

 # Symbolic algebra: examples: simplify.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests=>3;

  

 my ($x, $v, $t) = symbols(qw(x v t));

 

 ok(   ($v eq $x / $t)->solve(qw(x in terms of v t))  ==  $v*$t  );      

 ok(   ($v eq $x / $t)->solve(qw(x in terms of v t))  !=  $v/$t  );      

 ok(   ($v eq $x / $t)->solve(qw(x in terms of v t)) <=> '$v*$t' );



B<solve()> assumes that the equation on the left hand side is equal to

zero, applies various simplifications, then attempts to rearrange the

equation to obtain an equation for the first variable in the parameter

list assuming that the other terms mentioned in the parameter list are

known constants. There may of course be other unknown free variables in

the equation to be solved: the proposed solution is automatically tested

against the original equation to check that the proposed solution

removes these variables, an error is reported via B<die()> if it does not.

Example t/solve.t


 #!perl -w -I..

 #______________________________________________________________________

 # Symbolic algebra: quadratic equation.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::Simple tests => 2;

 

 my ($x) = symbols(qw(x));

 

 my  $p = $x**2-5*$x+6;        # Quadratic polynomial

 my ($a, $b) = @{($p > $x )};  # Solve for x

 

 print "x=$a,$b\n";            # Roots

 

 ok($a == 2);

 ok($b == 3);



If there are multiple solutions, (as in the case of polynomials), B<solve()>

returns an array of symbolic expressions containing the solutions.



=head3 Methods for performing Calculus

Differentiation: d()




Example t/differentiation.t

 #!perl -w -I..

 #______________________________________________________________________

 # Symbolic algebra.

 # PhilipRBrenan@yahoo.com, 2004, Perl License.

 #______________________________________________________________________

 

 use Math::Algebra::Symbols;

 use Test::More tests => 5;

 

 $x = symbols(qw(x));

            

 ok(  sin($x)    ==  sin($x)->d->d->d->d);

 ok(  cos($x)    ==  cos($x)->d->d->d->d);

 ok(  exp($x)    ==  exp($x)->d($x)->d('x')->d->d);

 ok( (1/$x)->d   == -1/$x**2);

 ok(  exp($x)->d->d->d->d <=> 'exp($x)' );



B<d()> differentiates the equation on the left hand side by the named

variable.

The variable to be differentiated by may be explicitly specified, either as a string or as single symbol; or it may be heuristically guessed as follows:

If the equation to be differentiated refers to only one symbol, then that symbol is used. If several symbols are present in the equation, but only one of t, x, y, z is present, then that variable is used in honor of Newton, Leibnitz, Cauchy.




=head2 Example of Equation Solving: the focii of a hyperbola:



 use Math::Algebra::Symbols;

 my ($a, $b, $x, $y, $i, $o) = symbols(qw(a b x y i 1));

 print

 "Hyperbola: Constant difference between distances from focii to locus of y=1/x",

 "\n  Assume by symmetry the focii are on ",

 "\n    the line y=x:                     ",  $f1 = $x + $i * $x,

 "\n  and equidistant from the origin:    ",  $f2 = -$f1,

 "\n  Choose a convenient point on y=1/x: ",  $a = $o+$i,

 "\n        and a general point on y=1/x: ",  $b = $y+$i/$y,

 "\n  Difference in distances from focii",

 "\n    From convenient point:            ",  $A = abs($a - $f2) - abs($a - $f1),  

 "\n    From general point:               ",  $B = abs($b - $f2) + abs($b - $f1),

 "\n\n  Solving for x we get:            x=", ($A - $B) > $x,

 "\n                         (should be: sqrt(2))",                        

 "\n  Which is indeed constant, as was to be demonstrated\n";

This example demonstrates the power of symbolic processing by finding the focii of the curve y=1/x, and incidentally, demonstrating that this curve is a hyperbola.




=head1 EXPORTS



 use Math::Algebra::Symbols

   symbols=>'S',

   trig   => 1,

   hyper  => 1,

   complex=> 1;



=over

trig=>0



The default, do not export trigonometric functions.



=item trig=>1



Export trigonometric functions: B<tan>, B<sec>, B<csc>, B<cot> to the

caller's namespace. B<sin>, B<cos> are created by default by overloading

the existing Perl B<sin> and B<cos> operators.



=item B<trigonometric>



Alias of B<trig>



=item hyperbolic=>0



The default, do not export hyperbolic functions.



=item hyper=>1



Export hyperbolic functions: B<sinh>, B<cosh>, B<tanh>, B<sech>,

B<csch>, B<coth> to the caller's namespace.



=item B<hyperbolic>



Alias of B<hyper>



=item complex=>0



The default, do not export complex functions



=item complex=>1



Export complex functions: B<conjugate>, B<cross>, B<dot>, B<im>,

B<modulus>, B<re>, B<unit> to the caller's namespace.



=back


PACKAGES




The B<Symbols> packages manipulate a sum of products representation of

an algebraic equation. The B<Symbols> package is the user interface to

the functionality supplied by the B<Symbols::Sum> and B<Symbols::Term>

packages.



=head2 Math::Algebra::Symbols::Term



B<Symbols::Term> represents a product term. A product term consists of the

number B<1>, optionally multiplied by:



=over

Variables



any number of variables raised to integer powers,



=item Coefficient



An integer coefficient optionally divided by a positive integer divisor,

both represented as BigInts if necessary.



=item Sqrt



The sqrt of of any symbolic expression representable by the B<Symbols>

package, including minus one: represented as B<i>.



=item Reciprocal



The multiplicative inverse of any symbolic expression representable by

the B<Symbols> package: i.e. a B<SymbolsTerm> may be divided by any

symbolic expression representable by the B<Symbols> package.



=item Exp



The number B<e> raised to the power of any symbolic expression

representable by the B<Symbols> package.



=item Log



The logarithm to base B<e> of any symbolic expression representable by

the B<Symbols> package.



=back



Thus B<SymbolsTerm> can represent expressions like:

  2/3*$x**2*$y**-3*exp($i*$pi)*sqrt($z**3) / $x

but not:


  $x + $y

for which package Symbols::Sum is required.

Math::Algebra::Symbols::Sum




B<Symbols::Sum> represents a sum of product terms supplied by

B<Symbols::Term> and thus behaves as a polynomial. Operations such as

equation solving and differentiation are applied at this level.

The main benefit of programming Symbols::Term and Symbols::Sum as two separate but related packages is Object Oriented Polymorphism. I.e. both packages need to multiply items together: each package has its own multiply method, with Perl method lookup selecting the appropriate one as required.




=head2 Math::Algebra::Symbols



Packaging the user functionality alone and separately in package

B<Symbols> allows the internal functions to be conveniently hidden from

user scripts.


AUTHOR




Philip R Brenan at B<philiprbrenan@yahoo.com>




=head2 Credits

Author




philiprbrenan@yahoo.com



=head3 Copyright



philiprbrenan@yahoo.com, 2004



=head3 License



Perl License.
Programminig
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Programming
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