Using equationsToMatrix( ) with symbolic variables representing derivatives

Currently trying to put a system of equations into matrix form. There is a function y1 (function of x(t)) that is differentiated twice, and then a function y2 (function of z(t)) differentiated once. With these derivations, the chain rule is being applied, so the derivatives of the x and z variables are becoming present. For this example problem, after being differentiated, they should be put into a matrix as follows:

[A][x_ddot; z_dot] = [b]

where [A] is a 1x2 matrix of coefficients to x_ddot and z_dot, and [b] is the rest of the equation (function of other variables/derivatives of variables). Here is the current code:

syms t x(t) z(t)         % define symbolic variables

y1     = x^3             % expression for y1 where x is a function of time
y1dot  = diff(y1,t)      % differentiation of y1 
y1ddot = diff(y1dot,t)   % differentiation of y1_ddot 
eqn1 = 2*y1ddot == 4     % equation 1

y2    = z^4             % expression for y2 where z is a function of time    
y2dot = diff(y2,t)      % differentiation of y2
eqn2 = 3*y2dot == 17    % equation 2

eqns = [eqn1; eqn2]     % system of equations to put into matrix form
vars = [sym(diff(x,2)); sym(diff(z,1))] % array of variables to sort each equation by in symbolic form
[A,b] = equationsToMatrix(eqns,vars) % equationsToMatrix expression

The expected output should look like this:

[6*x^2, 12z^3]*[x_ddot; z_dot] = [4-12*x*x_dot^2; 17]

I'm currently getting an error saying "Second argument must be a vector of symbolic variables." Is there a way to properly have the equationsToMatrix command use derivatives (like x_ddot and z_dot) to sort the matrices by? The syntax I used of sym(diff(x,2)) seemed to work for the built in isolate function, but not for thie equationsToMatrix.

[Dominik Huber]

Hello,

have the same problem. Were you able to find a solution for this problem?