equations_gauss.pl : Solves linear polynomial equations Solves linear polynomial equations by Gaussian variable elimination.
How to use: The handler solves a set of equations enclosed in curly brackets: {PL1=PR1, PL2=PR2, .., PLn=PRn}. (PLi, PRi are linear polynomial terms) If no solution exists the handler fails. Variables can either be expressed by Prolog variables (X) or by atoms (x). If Prolog variables are used, as soon as the handler has determined the value of a variable it is bound to this value, e.g.: X = 10. For Prolog variables, the termination of the handler requires a stable variable order that is implemented by the imported module var_order. If you don't want to use this module, you can also use atoms for this purpose, a variable binding is then represented as a normalized equation, e.g.: [1*x] eq 10.
Program: Change the code, then submit! /* equations_gauss.pl: Solves linear polynomial equations (C) Thom.Fruehwirth at uni-ulm.de, 1991-1998 (C) Christian Holzbaur, 1996 (C) Martin.Kaeser at uni-ulm.de, 2006/12/01 This program is distributed under the terms of the GNU General Public License: http://www.gnu.org/licenses/gpl.html %% DESCRIPTION Solves linear polynomial equations by Gaussian variable elimination. %% HOW TO USE The handler solves a set of equations enclosed in curly brackets:# *{PL1=PR1, PL2=PR2, .., PLn=PRn}.* (PLi, PRi are linear polynomial terms)# If no solution exists the handler fails. Variables can either be expressed by Prolog variables (X) or by atoms (x).# If Prolog variables are used, as soon as the handler has determined the value of a variable it is bound to this value, e.g.: X = 10.# For Prolog variables, the termination of the handler requires a stable variable order that is implemented by the imported module 'var_order'.# If you don't want to use this module, you can also use atoms for this purpose, a variable binding is then represented as a normalized equation, e.g.: *[1*x] eq 10.* %% SAMPLE QUERIES Q: {x+y=10, x-y=6}. A: [1*x]eq 8.0, [1*y]eq 2.0. Q: {X+Y=10, X-Y=6}. A: X = 8.0, Y = 2.0. Q: {X+Y=10, X+Y=6}. A: no. Q: {3 * X + 2 * Y - 4 * (3 + Z) = 2 * (X - 3) + (Y + Z) * 7, 2 * (X + Y + Z) = 3 * (X - Y - Z), 5 * (X + Y) - 7 * X - Z = (2 + 1 + X) * 6}. A: X = -1.7142857142857144, Y = 0.6571428571428571, Z = -1.0. Q: {3 * X + 2 * Y - 4 * (3 + Z) = 2 * (X - 3) + (Y + Z) * 7, 2 * (X + Y + Z) = 3 * (X - Y - Z)}. A: Z = -1.0, [1*X,-5*Y]eq-5.0. Q: {2+2*X+4*Y+2*Z=0, 4+2*X+4*Y+4*Z=0, 1+2*X+3*Z=0}. A: X = 1.0, Y = -0.5, Z = -1.0. Q: {-10+1*X+1*Y=0, 2+1*X+(-1)*Y=0}. A: X = 4.0, Y = 6.0. Q: {-10+1*X+1*Y=0, 2+1*X+(-1)*Y=0, -4+1*X=0}. A: X = 4.0, Y = 6.0. Q: {-10+1*X+1*Y=0, 2+1*X+(-1)*Y=0, -5+1*X=0}. A: no. Q: {-1+1*X+1*Y=0, -2+2*X+2*Y=0}. A: [1*X,1*Y]eq 1 ? Q: {X=Y+Z, X+Z=10, Y=10}. A: X = 10.0, Y = 10, Z = 0.0. Q: {X+Y=10, X-Z=20, 2*Y+Z=30}. A: X = -30.0, Y = 40.0, Z = -50.0. Q: {-(X)+Y+Z+2*Y+X+3*X+2=12}. A: [1*X,1.0*Y,0.3333333333333333*Z]eq 3.333333333333333. */ :- module(equations_gauss, [eq/2, {}/1]). :- use_module(library(chr)). :- use_module(library(lists)). user:library_directory('.'). :- use_module(library(var_order)). :- op(600,xfx,eq). %% Deprecated syntax used for SICStus 3.x %handler gauss. %constraints eq/2, {}/1. %% Syntax for SWI / SICStus 4.x :- chr_constraint eq/2, {}/1. %% Poly eq Const, where Poly is list of monomials Coefficient*Variable %% eq/2 %% curly brackets as wrapper to avoid name clash with built-in = %% {}/1 %% split system of equations split @ {E, F} <=> {E}, {F}. %% convert arbitrary polynomial equation to eq-notation normalize @ {A = B} <=> globalize([A-B]), normpoly([A-B] eq 0, Poly eq Const), Poly eq Const. %% 0=C zero @ [] eq C <=> zero(C). %% normalize first coefficient to 1 norm1 @ [A*X|P] eq C <=> notzero(A-1) | multpoly(1/A,P eq C,P2 eq C2), [1*X|P2] eq C2. %% const on left side (because of bound variable) bound @ P eq C <=> select(A*X, P, P0), number(X) | C0 is C-A*X, P0 eq C0. %% A*X = C => bind variable bind @ [A*X] eq C <=> var(X) | X is C/A. %% Gaussian elimination elimate @ [A*X|P] eq C \ Q eq D <=> select(B*X, Q, Q1) | multpoly(-B/A, P eq C, E), addpoly(E, Q1 eq D, Q0 eq D0), Q0 eq D0. %% Auxiliary predicates %% stable variable order based on chr/ordering by C. Holzbaur (var_order.pl) %% compare variables with var_compare ord_lss(X,Y) :- var_compare(<,X,Y). %% otherwise use Prolog standard order ord_lss(X,Y) :- nonvar(Y), X @< Y. %% numerical stabilty notzero(A) :- abs(A) > 0.000001. zero(A) :- abs(A) =< 0.000001. %% safe_is(X,Exp): X is Exp; fails, if Exp is not an arith. expression safe_is(X,Exp) :- on_exception(_, X is Exp, fail). %% normalize polynomial equation normpoly([X] eq C, [1*X] eq C) :- var(X), !. normpoly([X] eq C, [1*X] eq C) :- simple(X), \+ number(X). normpoly([A] eq C, [] eq C0) :- number(A), C0 is C-A. normpoly([A,B|P] eq C, E0) :- normpoly([A] eq 0,E1), normpoly([B|P] eq C,E2), addpoly(E1,E2,E0). normpoly([+A] eq 0, E0) :- normpoly([A] eq 0, E0). normpoly([-A] eq 0, E0) :- normpoly([A] eq 0, E1), multpoly(-1, E1, E0). normpoly([A+B] eq C, E0) :- normpoly([A] eq C,E), normpoly([B] eq 0,F), addpoly(E,F,E0). normpoly([A-B] eq C, E0) :- normpoly([A] eq C,E), normpoly([B] eq 0,F), multpoly(-1,F,F1), addpoly(E,F1,E0). normpoly([A*X] eq 0, E0) :- safe_is(A1,A), normpoly([X] eq 0, E), multpoly(A1,E,E0). normpoly([X*A] eq 0, E0) :- safe_is(A1,A), normpoly([X] eq 0, E), multpoly(A1,E,E0). normpoly([X/A] eq 0, E0) :- safe_is(A1,1/A), normpoly([X] eq 0, E), multpoly(A1,E,E0). normpoly([A] eq C, P0 eq C0) :- C\==0, normpoly([A] eq 0, P0 eq C1), C0 is C+C1. %% addpoly(E,F, E0): add polynomial equations %% requires: polynomials ordered + duplicate free; retains properties addpoly(P eq C, [] eq D, P eq C0) :- !, C0 is C+D. addpoly([] eq C, Q eq D, Q eq C0) :- !, C0 is C+D. addpoly([A*X|P] eq C, [B*Y|Q] eq D, E0) :- X==Y, !, A1 is A+B, addpoly(P eq C, Q eq D, P1 eq C1), (zero(A1) -> E0 = P1 eq C1 ; E0 = [A1*X|P1] eq C1). addpoly([A*X|P] eq C, [B*Y|Q] eq D, [A*X|P0] eq C0) :- ord_lss(X,Y), !, addpoly(P eq C, [B*Y|Q] eq D, P0 eq C0). addpoly([A*X|P] eq C, [B*Y|Q] eq D, [B*Y|P0] eq C0) :- ord_lss(Y,X), !, addpoly([A*X|P] eq C, Q eq D, P0 eq C0). %% multpoly(M,E, E0): multiply polynomial equation with scalar multpoly(M, [] eq C, [] eq C0) :- C0 is M*C. multpoly(M, [A*X|P] eq C, E0) :- A1 is M*A, multpoly(M,P eq C,P1 eq C1), (zero(A1) -> E0 = P1 eq C1 ; E0 = [A1*X|P1] eq C1).
Console: Enter query or select example from below, then submit and wait for answer! % loading solvers/equations_gauss.pl | ?- consult(...). yes [0.277 seconds] | ?-