## Symbolic three-equation system, three variables to first derivative of each variable in each equation

### VincentLec (view profile)

on 13 Jun 2016
Latest activity Commented on by VincentLec

on 13 Jun 2016

### Walter Roberson (view profile)

Hello, I have this symbolic equation system:
Eqn1 = A(t)*x(t) + B(t)*y(t) C(t)*z(t) + D(t)*dx(t)/dt + E(t)*dy(t)/dt + F(t)*dz(t)/dt == f1(t);
Eqn2 = G(t)*x(t) + H(t)*y(t) I(t)*z(t) + J(t)*dx(t)/dt + K(t)*dy(t)/dt + L(t)*dz(t)/dt == f2(t);
Eqn3 = M(t)*x(t) + N(t)*y(t) P(t)*z(t) + Q(t)*dx(t)/dt + R(t)*dy(t)/dt + S(t)*dz(t)/dt == f3(t);
Of course, I know the formulas of A(t)..S(t) as well as the formulas of f1(t), f2(t) and f3(t) (they are just way too long to copy-paste here)
Now, my goal is to determine the formulas of x(t), y(t) and z(t) and I have absolutely no idea how to proceed... Also, not sure if that helps, but all the equations are sin and cos functions.
Thanks a bunch for all of your help

### Tags ### Walter Roberson (view profile)

on 13 Jun 2016

You can use the Symbolic Toolbox dsolve() .
However, if the formula are complicated, it would be common for dsolve to not be able to find a solution. Differential equations can be difficult to solve symbolically.

VincentLec

### VincentLec (view profile)

on 13 Jun 2016
Would converting the symbolic function to a MatLab Function using matlabFunction make it easier for Matlab to solve them? For example, what if I did
eqn11 = matlabFunction(eqn1)
eqn22 = matlabFunction(eqn2)
eqn33 = matlabFunction(eqn3)
before using dsolve().
Walter Roberson

### Walter Roberson (view profile)

on 13 Jun 2016
No, dsolve() is strictly symbolic and matlabFunction is for creating numeric routines (e.g., routines you might use with one of the ode* functions.)
VincentLec

### VincentLec (view profile)

on 13 Jun 2016
Ok, I'll try to see what I can do. Thanks!