MATLAB: Solving equation written in the functions

equationfsolveMATLABvpasolve

I want to solve three equations with three unknowns.

Force_x(x,y,z) == 0, Force_y(x,y,z) == 0, Force_z(x,y,z) == 0

Where Force_x(x,y,z) etc are functions defined in anothe file which involves x, y, z.

vpasolve is not working here because Force_x works only when x y z are numbers, while vpasolve is passing symbols.

Help me with any other method or any modification.

my code:

[XX, YY] = vpasolve([Force_x(x,y,z)==0, Force_y(x,y,z)==0, Force_z(x,y,z)==0], [x, y, z], [0, 0, 0]);

error: Invalid arguments specified in evaluating the interpolant.

this error is due to symbols passed by Force_x.

Best Answer

 fsolve(@(V) [Force_x(V(1),V(2),V(3)), Force_y(V(1),V(2),V(3)), Force_z(V(1),V(2),V(3))], [0 0 0])

Related Solutions

MATLAB: Solving equation written in the functions

Hi,

You can try following code:

syms x y z Force_x Force_y Force_z
[X Y Z] = vpasolve([Force_x==0,Force_y==0,Force_z ==0],[x y z],[0 0 0])

This would start produce generic output as shown :

X =
 
Empty sym: 0-by-1
 
 
Y =
 
Empty sym: 0-by-1
 
 
Z =
 
Empty sym: 0-by-1

See this if it matches the requirement in output. Once you start calling function Force_x and other two then it should start outputting correct value.

Hope it helps !

MATLAB: Needs derivative w.r.t. ‘ y ‘ & then graph w.r.t ‘ t ‘

diff is a function of the symbolic package, so when you try to derivate U, you are derivating a constant, and by a constant, so F is a 0. To do what you want, you should do it in symbolic and then replace your variable, like:

syms y t
P2=5;           
U=exp(y*sqrt(P2)).*(1-erf(y./(2.*sqrt(t))+ sqrt(P2.*t)));
S= - diff(U,y); 
v_t=0.01:0.01:5;
F = subs(S,y,0);
plot(v_t,vpa(subs(F,t,v_t)))
xlabel(' t');
ylabel('F');

Best Answer

Related Solutions

MATLAB: Solving equation written in the functions

MATLAB: Needs derivative w.r.t. ‘ y ‘ & then graph w.r.t ‘ t ‘

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