Force symbolic simplification to eliminate variable

When breaking down a (long and complex) formula into the form , I use the approach of the lincoeffs script.

The problem is, that I still have u in b, because simplification isn't detecting that the terms cancel out.

Is there a trick to force the elimination of u-terms?

The symbolic expression is attached if you want to try it, the code is as follows:

% NOT WORKING - extract coefficients of ddddh_fun
syms u
% ddddh_fun = expand(ddddh_fun);
ddddh_fun_formula = formula(ddddh_fun) == 0;
[ddddh_fun_A,ddddh_fun_b] = lincoeffs(ddddh_fun_formula,u)
ddddh_fun_b = simplify(ddddh_fun_b,'Steps',50);

---

% WORKING - extract coefficients of ddddh_fun
syms u
ddddh_fun = expand(ddddh_fun);
ddddh_fun_formula = formula(ddddh_fun) == 0;
[ddddh_fun_A,ddddh_fun_b] = lincoeffs(ddddh_fun_formula,u)
ddddh_fun_b = simplify(ddddh_fun_b,'Steps',50);

The problem with this is, that the very expanded expression from the working version isn't very readable when I do export is as Latex, which is necessary for me.

To read the symbolic function and the matlabFunction derived from this is also very hard this way.

Answer 1

[Paul]

Hi ludolfusexe,

Try equationsToMatrix

load ddddh_fun
symvar(ddddh_fun)

ans = 

syms u
% A*u = b
[A,b] = equationsToMatrix(ddddh_fun == 0,u)

A = 

b = 

Verify that A and b do not depend on u

symvar(A)

ans = 

symvar(b)

ans = 

Reverse sign of b for desired form: A*u + b = 0

b = -b;

Verify

simplify(ddddh_fun - (A*u + b))

ans(t) = 

0

[ludolfusexe]

Thank you for your reply, the solution is exactly what I was looking for.