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[maxima.git] / tests / wester_problems / test_equations.mac

/* Original version of this file copyright 1999 by Michael Wester,
 * and retrieved from http://www.math.unm.edu/~wester/demos/Equations/problems.macsyma
 * circa 2006-10-23.
 *
 * Released under the terms of the GNU General Public License, version 2,
 * per message dated 2007-06-03 from Michael Wester to Robert Dodier
 * (contained in the file wester-gpl-permission-message.txt).
 *
 * See: "A Critique of the Mathematical Abilities of CA Systems"
 * by Michael Wester, pp 25--60 in
 * "Computer Algebra Systems: A Practical Guide", edited by Michael J. Wester
 * and published by John Wiley and Sons, Chichester, United Kingdom, 1999.
 */
/* ----------[ M a c s y m a ]---------- */
/* ---------- Initialization ---------- */
showtime: all$
prederror: false$
/* ---------- Equations ---------- */
/* Manipulate an equation using a natural syntax:
   (x = 2)/2 + (1 = 1) => x/2 + 1 = 2 */
(x = 2)/2 + (1 = 1);
/* Solve various nonlinear equations---this cubic polynomial has all real roots
   */
solve(3*x^3 - 18*x^2 + 33*x - 19 = 0, x);
ratsimp(rectform(%));
/* Some simple seeming problems can have messy answers:
   x = {  [sqrt(5) - 1]/4 +/- 5^(1/4) sqrt(sqrt(5) + 1)/[2 sqrt(2)] i,
        - [sqrt(5) + 1]/4 +/- 5^(1/4) sqrt(sqrt(5) - 1)/[2 sqrt(2)] i} */
eqn: x^4 + x^3 + x^2 + x + 1 = 0;
solve(eqn, x);
/* Check one of the answers */
ev(eqn, %[1]);
radcan(%);
remvalue(eqn)$
/* x = {2^(1/3) +- sqrt(3), +- sqrt(3) - 1/2^(2/3) +- i sqrt(3)/2^(2/3)} 
       [Mohamed Omar Rayes] */
solve(x^6 - 9*x^4 - 4*x^3 + 27*x^2 - 36*x - 23 = 0, x);
/* x = {1, e^(+- 2 pi i/7), e^(+- 4 pi i/7), e^(+- 6 pi i/7)} */
solve(x^7 - 1 = 0, x);
/* x = 1 +- sqrt(+-sqrt(+-4 sqrt(3) - 3) - 3)/sqrt(2)   [Richard Liska] */
solve(x^8 - 8*x^7 + 34*x^6 - 92*x^5 + 175*x^4 - 236*x^3 + 226*x^2 - 140*x + 46
      = 0, x);
/* The following equations have an infinite number of solutions (let n be an
   arbitrary integer):
   x = {log(sqrt(z) - 1), log(sqrt(z) + 1) + i pi} [+ n 2 pi i, + n 2 pi i] */
%e^(2*x) + 2*%e^x + 1 = z;
solve(%, x);
/* x = (1 +- sqrt(9 - 8 n pi i))/2.  Real solutions correspond to n = 0 =>
   x = {-1, 2} */
solve(exp(2 - x^2) = exp(-x), x);
/* x = -W[n](-1) [e.g., -W[0](-1) = 0.31813 - 1.33724 i] where W[n](x) is the
   nth branch of Lambert's W function */
solve(exp(x) = x, x);
/* x = {-1, 1} */
solve(x^x = x, x);
/* This equation is already factored and so *should* be easy to solve:
   x = {-1, 2*{+-arcsinh(1) i + n pi}, 3*{pi/6 + n pi/3}} */
(x + 1) * (sin(x)^2 + 1)^2 * cos(3*x)^3 = 0;
solve(%, x);
multiplicities;
/* x = pi/4 [+ n pi] */
solve(sin(x) = cos(x), x);
solve(tan(x) = 1, x);
/* x = {pi/6, 5 pi/6} [ + n 2 pi, + n 2 pi ] */
solve(sin(x) = 1/2, x);
/* x = {0, 0} [+ n pi, + n 2 pi] */
solve(sin(x) = tan(x), x);
multiplicities;
/* x = {0, 0, 0} */
solve(asin(x) = atan(x), x);
multiplicities;
/* x = sqrt[(sqrt(5) - 1)/2] */
solve(acos(x) = atan(x), x);
/* x = 2 */
solve((x - 2)/x^(1/3) = 0, x);
/* This equation has no solutions */
solve(sqrt(x^2 + 1) = x - 2, x);
/* x = 1 */
solve(x + sqrt(x) = 2, x);
/* x = 1/16 */
solve(2*sqrt(x) + 3*x^(1/4) - 2 = 0, x);
/* x = {sqrt[(sqrt(5) - 1)/2], -i sqrt[(sqrt(5) + 1)/2]} */
solve(x = 1/sqrt(1 + x^2), x);
/* This problem is from a computational biology talk => 1 - log_2[m (m - 1)] */
solve(binomial(m, 2)*2^k = 1, k);
/* x = log(c/a) / log(b/d) for a, b, c, d != 0 and b, d != 1   [Bill Pletsch] */
solve(a*b^x = c*d^x, x);
logcontract(%);
/* x = {1, e^4} */
errcatch(solve(sqrt(log(x)) = log(sqrt(x)), x));
/* Recursive use of inverses, including multiple branches of rational
   fractional powers   [Richard Liska]
   => x = +-(b + sin(1 + cos(1/e^2)))^(3/2) */
assume(sin(cos(1/%e^2) + 1) + b > 0)$
solve(log(acos(asin(x^(2/3) - b) - 1)) + 2 = 0, x);
forget(sin(cos(1/%e^2) + 1) + b > 0)$
/* x = {-0.784966, -0.016291, 0.802557}  From Metha Kamminga-van Hulsen,
   ``Hoisting the Sails and Casting Off with Maple'', _Computer Algebra
   Nederland Nieuwsbrief_, Number 13, December 1994, ISSN 1380-1260, 27--40. */
eqn: 5*x + exp((x - 5)/2) = 8*x^3;
solve(eqn, x);
root_by_bisection(eqn, x, -1,  -0.5);
root_by_bisection(eqn, x, -0.5, 0.5);
root_by_bisection(eqn, x,  0.5, 1);
remvalue(eqn)$
/* x = {-1, 3} */
solve(abs(x - 1) = 2, x);
/* x = {-1, -7} */
solve(abs(2*x + 5) = abs(x - 2), x);
/* x = +-3/2 */
solve(1 - abs(x) = max(-x - 2, x - 2), x);
/* x = {-1, 3} */
solve(max(2 - x^2, x) = max(-x, x^3/9), x);
/* x = {+-3, -3 [1 + sqrt(3) sin t + cos t]} = {+-3, -1.554894}
   where t = (arctan[sqrt(5)/2] - pi)/3.  The third answer is the root of
   x^3 + 9 x^2 - 18 = 0 in the interval (-2, -1). */
solve(max(2 - x^2, x) = x^3/9, x);
/* z = 2 + 3 i */
declare(z, complex)$
eqn: (1 + %i)*z + (2 - %i)*conjugate(z) = -3*%i;
solve(eqn, z);
declare([x, y], real)$
subst(z = x + %i*y, eqn);
ratsimp(ev(%, conjugate));
solve(%, [x, y]);
remove([x, y], real, z, complex)$
remvalue(eqn)$
/* => {f^(-1)(1), f^(-1)(-2)} assuming f is invertible */
solve(f(x)^2 + f(x) - 2 = 0, x);
remvalue(eqns, vars)$
/* Solve a 3 x 3 system of linear equations */
eqn1:   x +   y +   z =  6;
eqn2: 2*x +   y + 2*z = 10;
eqn3:   x + 3*y +   z = 10;
/* Note that the solution is parametric: x = 4 - z, y = 2 */
solve([eqn1, eqn2, eqn3], [x, y, z]);
/* A linear system arising from the computation of a truncated power series
   solution to a differential equation.  There are 189 equations to be solved
   for 49 unknowns.  42 of the equations are repeats of other equations; many
   others are trivial.  Solving this system directly by Gaussian elimination
   is *not* a good idea.  Solving the easy equations first is probably a better
   method.  The solution is actually rather simple.   [Stanly Steinberg]
   => k1 = ... = k22 = k24 = k25 = k27 = ... = k30 = k32 = k33 = k35 = ...
      = k38 = k40 = k41 = k44 = ... = k49 = 0, k23 = k31 = k39,
      k34 = b/a k26, k42 = c/a k26, {k23, k26, k43} are arbitrary */
eqns: [
 -b*k8/a+c*k8/a = 0, -b*k11/a+c*k11/a = 0, -b*k10/a+c*k10/a+k2 = 0,
 -k3-b*k9/a+c*k9/a = 0, -b*k14/a+c*k14/a = 0, -b*k15/a+c*k15/a = 0,
 -b*k18/a+c*k18/a-k2 = 0, -b*k17/a+c*k17/a = 0, -b*k16/a+c*k16/a+k4 = 0,
 -b*k13/a+c*k13/a-b*k21/a+c*k21/a+b*k5/a-c*k5/a = 0, b*k44/a-c*k44/a = 0,
 -b*k45/a+c*k45/a = 0, -b*k20/a+c*k20/a = 0, -b*k44/a+c*k44/a = 0,
  b*k46/a-c*k46/a = 0, b^2*k47/a^2-2*b*c*k47/a^2+c^2*k47/a^2 = 0, k3 = 0,
 -k4 = 0, -b*k12/a+c*k12/a-a*k6/b+c*k6/b = 0,
 -b*k19/a+c*k19/a+a*k7/c-b*k7/c = 0, b*k45/a-c*k45/a = 0,
 -b*k46/a+c*k46/a = 0, -k48+c*k48/a+c*k48/b-c^2*k48/(a*b) = 0,
 -k49+b*k49/a+b*k49/c-b^2*k49/(a*c) = 0, a*k1/b-c*k1/b = 0,
  a*k4/b-c*k4/b = 0, a*k3/b-c*k3/b+k9 = 0, -k10+a*k2/b-c*k2/b = 0,
  a*k7/b-c*k7/b = 0, -k9 = 0, k11 = 0, b*k12/a-c*k12/a+a*k6/b-c*k6/b = 0,
  a*k15/b-c*k15/b = 0, k10+a*k18/b-c*k18/b = 0, -k11+a*k17/b-c*k17/b = 0,
  a*k16/b-c*k16/b = 0, -a*k13/b+c*k13/b+a*k21/b-c*k21/b+a*k5/b-c*k5/b = 0,
 -a*k44/b+c*k44/b = 0, a*k45/b-c*k45/b = 0,
  a*k14/c-b*k14/c+a*k20/b-c*k20/b = 0, a*k44/b-c*k44/b = 0,
 -a*k46/b+c*k46/b = 0, -k47+c*k47/a+c*k47/b-c^2*k47/(a*b) = 0,
  a*k19/b-c*k19/b = 0, -a*k45/b+c*k45/b = 0, a*k46/b-c*k46/b = 0,
  a^2*k48/b^2-2*a*c*k48/b^2+c^2*k48/b^2 = 0,
 -k49+a*k49/b+a*k49/c-a^2*k49/(b*c) = 0, k16 = 0, -k17 = 0,
 -a*k1/c+b*k1/c = 0, -k16-a*k4/c+b*k4/c = 0, -a*k3/c+b*k3/c = 0,
  k18-a*k2/c+b*k2/c = 0, b*k19/a-c*k19/a-a*k7/c+b*k7/c = 0,
 -a*k6/c+b*k6/c = 0, -a*k8/c+b*k8/c = 0, -a*k11/c+b*k11/c+k17 = 0,
 -a*k10/c+b*k10/c-k18 = 0, -a*k9/c+b*k9/c = 0,
 -a*k14/c+b*k14/c-a*k20/b+c*k20/b = 0,
 -a*k13/c+b*k13/c+a*k21/c-b*k21/c-a*k5/c+b*k5/c = 0, a*k44/c-b*k44/c = 0,
 -a*k45/c+b*k45/c = 0, -a*k44/c+b*k44/c = 0, a*k46/c-b*k46/c = 0,
 -k47+b*k47/a+b*k47/c-b^2*k47/(a*c) = 0, -a*k12/c+b*k12/c = 0,
  a*k45/c-b*k45/c = 0, -a*k46/c+b*k46/c = 0,
 -k48+a*k48/b+a*k48/c-a^2*k48/(b*c) = 0,
  a^2*k49/c^2-2*a*b*k49/c^2+b^2*k49/c^2 = 0, k8 = 0, k11 = 0, -k15 = 0,
  k10-k18 = 0, -k17 = 0, k9 = 0, -k16 = 0, -k29 = 0, k14-k32 = 0,
 -k21+k23-k31 = 0, -k24-k30 = 0, -k35 = 0, k44 = 0, -k45 = 0, k36 = 0,
  k13-k23+k39 = 0, -k20+k38 = 0, k25+k37 = 0, b*k26/a-c*k26/a-k34+k42 = 0,
 -2*k44 = 0, k45 = 0, k46 = 0, b*k47/a-c*k47/a = 0, k41 = 0, k44 = 0,
 -k46 = 0, -b*k47/a+c*k47/a = 0, k12+k24 = 0, -k19-k25 = 0,
 -a*k27/b+c*k27/b-k33 = 0, k45 = 0, -k46 = 0, -a*k48/b+c*k48/b = 0,
  a*k28/c-b*k28/c+k40 = 0, -k45 = 0, k46 = 0, a*k48/b-c*k48/b = 0,
  a*k49/c-b*k49/c = 0, -a*k49/c+b*k49/c = 0, -k1 = 0, -k4 = 0, -k3 = 0,
  k15 = 0, k18-k2 = 0, k17 = 0, k16 = 0, k22 = 0, k25-k7 = 0,
  k24+k30 = 0, k21+k23-k31 = 0, k28 = 0, -k44 = 0, k45 = 0, -k30-k6 = 0,
  k20+k32 = 0, k27+b*k33/a-c*k33/a = 0, k44 = 0, -k46 = 0,
 -b*k47/a+c*k47/a = 0, -k36 = 0, k31-k39-k5 = 0, -k32-k38 = 0,
  k19-k37 = 0, k26-a*k34/b+c*k34/b-k42 = 0, k44 = 0, -2*k45 = 0, k46 = 0,
  a*k48/b-c*k48/b = 0, a*k35/c-b*k35/c-k41 = 0, -k44 = 0, k46 = 0,
  b*k47/a-c*k47/a = 0, -a*k49/c+b*k49/c = 0, -k40 = 0, k45 = 0, -k46 = 0,
 -a*k48/b+c*k48/b = 0, a*k49/c-b*k49/c = 0, k1 = 0, k4 = 0, k3 = 0,
 -k8 = 0, -k11 = 0, -k10+k2 = 0, -k9 = 0, k37+k7 = 0, -k14-k38 = 0,
 -k22 = 0, -k25-k37 = 0, -k24+k6 = 0, -k13-k23+k39 = 0,
 -k28+b*k40/a-c*k40/a = 0, k44 = 0, -k45 = 0, -k27 = 0, -k44 = 0,
  k46 = 0, b*k47/a-c*k47/a = 0, k29 = 0, k32+k38 = 0, k31-k39+k5 = 0,
 -k12+k30 = 0, k35-a*k41/b+c*k41/b = 0, -k44 = 0, k45 = 0,
 -k26+k34+a*k42/c-b*k42/c = 0, k44 = 0, k45 = 0, -2*k46 = 0,
 -b*k47/a+c*k47/a = 0, -a*k48/b+c*k48/b = 0, a*k49/c-b*k49/c = 0, k33 = 0,
 -k45 = 0, k46 = 0, a*k48/b-c*k48/b = 0, -a*k49/c+b*k49/c = 0
 ]$
vars: [k1, k2, k3, k4, k5, k6, k7, k8, k9, k10, k11, k12, k13, k14, k15, k16,
       k17, k18, k19, k20, k21, k22, k23, k24, k25, k26, k27, k28, k29, k30,
       k31, k32, k33, k34, k35, k36, k37, k38, k39, k40, k41, k42, k43, k44,
       k45, k46, k47, k48, k49]$
solve(eqns, vars);
/* Solve a 3 x 3 system of nonlinear equations */
eqn1: x^2*y + 3*y*z - 4 = 0;
eqn2: -3*x^2*z + 2*y^2 + 1 = 0;
eqn3: 2*y*z^2 - z^2 - 1 = 0;
/* Solving this by hand would be a nightmare */
solve([eqn1, eqn2, eqn3], [x, y, z]);
rectform(sfloat(%[1..5]));
remvalue(eqn1, eqn2, eqn3)$