symbolic equation Empty sym: 0-by-1
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here's the command line instruction I issue:-
solve('xw = xo+sin(xo)*180/pi',xo)
but I get:- ans = Empty sym: 0-by-1
I'm obviously new to Matlab...any help appreciated..Thanks
5 个评论
Walter Roberson
2018-3-18
When I test your equation with xw arbitrarily set to sqrt(2) or 10, I find 36 or 38 real solutions: which one did you need?
回答(2 个)
John D'Errico
2018-3-18
编辑:John D'Errico
2018-3-18
Being new is irrelevant. This is just a question of mathematics. Sym produces an empty result because there is no analytical solution to the problem posed. It is trivially simple to write an expression with no analytical solution. You just proved that by example.
If you have a specific value for xw, then use a tool like fzero or vpasolve, that will be able to provide a numerical root finding solution. Even there, you may need to beware, because there may be still no solution, or there may be multiple solutions, and the rootfinder will only provide a single solution. In the latter case, it will depend on the starting point for the solver.
qasem qasem
2020-8-10
here's the command line instruction I issue:-
syms a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18...
a19 a20
eqn0=-2*(-(e*a0)-x2*a1-x3*a2-x2*a3-x3*a4-x4*a5-x5*a6-x2*a7-x3*a8-x4*a9-...
x5*a10-x6*a11-x7*a12-x2*a13-x3*a14-x4*a15-x5*a16-x6*a17-x7*a18-x8*a19...
-x9*a20)==2*x1;
eqn1=-2*(-x2*a0-xx2*a1-xx3*a2-xx2*a3-xx3*a4-xx4*a5-xx5*a6-xx2*a7-xx3*a8-xx4*a9-...
xx5*a10-xx6*a11-xx7*a12-xx2*a13-xx3*a14-xx4*a15-xx5*a16-xx6*a17-xx7*a18-xx8*a19...
-xx9*a20)==2*xx1;
eqn2=-2*(-x3*a0-rr2*a1-rr3*a2-rr2*a3-rr3*a4-rr4*a5-rr5*a6-rr2*a7-rr3*a8-rr4*a9-...
rr5*a10-rr6*a11-rr7*a12-rr2*a13-rr3*a14-rr4*a15-rr5*a16-rr6*a17-rr7*a18-rr8*a19...
-rr9*a20)==2*rr1;
eqn3=-2*(-x2*a0-xx2*a1-xx3*a2-xx2*a3-xx3*a4-xx4*a5-xx5*a6-xx2*a7-xx3*a8-xx4*a9-...
xx5*a10-xx6*a11-xx7*a12-xx2*a13-xx3*a14-xx4*a15-xx5*a16-xx6*a17-xx7*a18-xx8*a19...
-xx9*a20)==2*xx1;
eqn4=-2*(-x3*a0-rr2*a1-rr3*a2-rr2*a3-rr3*a4-rr4*a5-rr5*a6-rr2*a7-rr3*a8-rr4*a9-...
rr5*a10-rr6*a11-rr7*a12-rr2*a13-rr3*a14-rr4*a15-rr5*a16-rr6*a17-rr7*a18-rr8*a19...
-rr9*a20)==2*rr1;
eqn5=-2*(-x4*a0-ww2*a1-ww3*a2-ww2*a3-ww3*a4-ww4*a5-ww5*a6-ww2*a7-ww3*a8-ww4*a9-...
ww5*a10-ww6*a11-ww7*a12-ww2*a13-ww3*a14-ww4*a15-ww5*a16-ww6*a17-ww7*a18-ww8*a19...
-ww9*a20)==2*ww1;
eqn6=-2*(-x5*a0-ee2*a1-ee3*a2-ee2*a3-ee3*a4-ee4*a5-ee5*a6-ee2*a7-ee3*a8-ee4*a9-...
ee5*a10-ee6*a11-ee7*a12-ee2*a13-ee3*a14-ee4*a15-ee5*a16-ee6*a17-ee7*a18-ee8*a19...
-ee9*a20)==2*ee1;
eqn7=-2*(-x2*a0-xx2*a1-xx3*a2-xx2*a3-xx3*a4-xx4*a5-xx5*a6-xx2*a7-xx3*a8-xx4*a9-...
xx5*a10-xx6*a11-xx7*a12-xx2*a13-xx3*a14-xx4*a15-xx5*a16-xx6*a17-xx7*a18-xx8*a19...
-xx9*a20)==xx1;
eqn8=-2*(-x3*a0-rr2*a1-rr3*a2-rr2*a3-rr3*a4-rr4*a5-rr5*a6-rr2*a7-rr3*a8-rr4*a9-...
rr5*a10-rr6*a11-rr7*a12-rr2*a13-rr3*a14-rr4*a15-rr5*a16-rr6*a17-rr7*a18-rr8*a19...
-rr9*a20)==2*rr1;
eqn9=-2*(-x4*a0-ww2*a1-ww3*a2-ww2*a3-ww3*a4-ww4*a5-ww5*a6-ww2*a7-ww3*a8-ww4*a9-...
ww5*a10-ww6*a11-ww7*a12-ww2*a13-ww3*a14-ww4*a15-ww5*a16-ww6*a17-ww7*a18-ww8*a19...
-ww9*a20)==2*ww1;
eqn10=-2*(-x5*a0-ee2*a1-ee3*a2-ee2*a3-ee3*a4-ee4*a5-ee5*a6-ee2*a7-ee3*a8-ee4*a9-...
ee5*a10-ee6*a11-ee7*a12-ee2*a13-ee3*a14-ee4*a15-ee5*a16-ee6*a17-ee7*a18-ee8*a19...
-ee9*a20)==2*ee1;
eqn11=-2*(-x6*a0-yy2*a1-yy3*a2-yy2*a3-yy3*a4-yy4*a5-yy5*a6-yy2*a7-yy3*a8-yy4*a9-...
yy5*a10-yy6*a11-yy7*a12-yy2*a13-yy3*a14-yy4*a15-yy5*a16-yy6*a17-yy7*a18-yy8*a19...
-yy9*a20)==2*yy1;
eqn12=-2*(-x7*a0-uu2*a1-uu3*a2-uu2*a3-uu3*a4-uu4*a5-uu5*a6-uu2*a7-uu3*a8-uu4*a9-...
uu5*a10-uu6*a11-uu7*a12-uu2*a13-uu3*a14-uu4*a15-uu5*a16-uu6*a17-uu7*a18-uu8*a19...
-uu9*a20)==2*uu1;
eqn13=-2*(-x2*a0-xx2*a1-xx3*a2-xx2*a3-xx3*a4-xx4*a5-xx5*a6-xx2*a7-xx3*a8-xx4*a9-...
xx5*a10-xx6*a11-xx7*a12-xx2*a13-xx3*a14-xx4*a15-xx5*a16-xx6*a17-xx7*a18-xx8*a19...
-xx9*a20)==2*xx1;
eqn14=-2*(-x3*a0-rr2*a1-rr3*a2-rr2*a3-rr3*a4-rr4*a5-rr5*a6-rr2*a7-rr3*a8-rr4*a9-...
rr5*a10-rr6*a11-rr7*a12-rr2*a13-rr3*a14-rr4*a15-rr5*a16-rr6*a17-rr7*a18-rr8*a19...
-rr9*a20)==2*rr1;
eqn15=-2*(-x4*a0-ww2*a1-ww3*a2-ww2*a3-ww3*a4-ww4*a5-ww5*a6-ww2*a7-ww3*a8-ww4*a9-...
ww5*a10-ww6*a11-ww7*a12-ww2*a13-ww3*a14-ww4*a15-ww5*a16-ww6*a17-ww7*a18-ww8*a19...
-ww9*a20)==2*ww1;
eqn16=-2*(-x5*a0-ee2*a1-ee3*a2-ee2*a3-ee3*a4-ee4*a5-ee5*a6-ee2*a7-ee3*a8-ee4*a9-...
ee5*a10-ee6*a11-ee7*a12-ee2*a13-ee3*a14-ee4*a15-ee5*a16-ee6*a17-ee7*a18-ee8*a19...
-ee9*a20)==2*ee1;
eqn17=-2*(-x6*a0-yy2*a1-yy3*a2-yy2*a3-yy3*a4-yy4*a5-yy5*a6-yy2*a7-yy3*a8-yy4*a9-...
yy5*a10-yy6*a11-yy7*a12-yy2*a13-yy3*a14-yy4*a15-yy5*a16-yy6*a17-yy7*a18-yy8*a19...
-yy9*a20)==2*yy1;
eqn18=-2*(-x7*a0-uu2*a1-uu3*a2-uu2*a3-uu3*a4-uu4*a5-uu5*a6-uu2*a7-uu3*a8-uu4*a9-...
uu5*a10-uu6*a11-uu7*a12-uu2*a13-uu3*a14-uu4*a15-uu5*a16-uu6*a17-uu7*a18-uu8*a19...
-uu9*a20)==2*uu1;
eqn19=-2*(-x8*a0-ii2*a1-ii3*a2-ii2*a3-ii3*a4-ii4*a5-ii5*a6-ii2*a7-ii3*a8-ii4*a9-...
ii5*a10-ii6*a11-ii7*a12-ii2*a13-ii3*a14-ii4*a15-ii5*a16-ii6*a17-ii7*a18-ii8*a19...
-ii9*a20)==2*ii1;
eqn20=-2*(-x9*a0-oo2*a1-oo3*a2-oo2*a3-oo3*a4-oo4*a5-oo5*a6-oo2*a7-oo3*a8-oo4*a9-...
oo5*a10-oo6*a11-oo7*a12-oo2*a13-oo3*a14-oo4*a15-oo5*a16-oo6*a17-oo7*a18-oo8*a19...
-oo9*a20)==2*oo1;
sol = solve(eqn0, eqn1, eqn2, eqn3, eqn4, eqn5, eqn6, eqn7, eqn8,...
eqn9, eqn10, eqn11, eqn12, eqn13, eqn14, eqn15, eqn16, eqn17, eqn18, eqn19, eqn20)
a0sol=double(sol.a0)
a1sol=double(sol.a1)
a2sol=double(sol.a2 )
a3sol=double(sol.a3 )
a4sol=double(sol.a4)
a5sol=double(sol.a5)
a6sol=double(sol.a6)
a7sol=double(sol.a7)
a8sol=double(sol.a8)
a9sol=double(sol.a9 )
a10sol=double(sol.a10 )
a11sol=double(sol.a11)
a12sol=double(sol.a12)
a13sol=double(sol.a13 )
a14sol=double(sol.a14 )
a15sol=double(sol.a15 )
a16sol=double(sol.a16)
a17sol=double(sol.a17)
a18sol=double(sol.a18)
a19sol=double(sol.a19)
a20sol=double(sol.a20)
but I get:- ans = Empty sym: 0-by-1
I'm obviously new to Matlab...any help appreciated..Thanks
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