What is causing Invalid variable 'conjugate(B(t))' in Symbolic Math Toolbox?

Question

winkmal 2019-1-22

0
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https://ww2.mathworks.cn/matlabcentral/answers/440885-what-is-causing-invalid-variable-conjugate-b-t-in-symbolic-math-toolbox

回答： Walter Roberson 2019-1-22

While trying to solve a DAE system with Symbolic Math Toolbox, I keep getting the same error. Unfortunately, the error message does not appear that much on the web. I am on Matlab R2018a.

Error using symengine
Invalid variable 'conjugate(B(t))'.

I did follow the example from Documentation exactly. Other ODEs work, but not this one. For instance, here is a working example:

% Differential Variables
syms A(t) B(t) C(t) D(t)
% Algebraic Variables
syms rho_1(t) rho_2(t) rho_3(t) rho_4(t)
% Model Parameters
syms k_1 k_2 k_3 k_4
diffEquations = [-rho_1(t) == diff(A(t), t),...
    2*rho_1(t) - 2*rho_2(t) + 2*rho_3(t) - rho_4(t) == diff(B(t), t),...
    rho_2(t) - rho_3(t) == diff(C(t), t),...
    rho_4(t) == diff(D(t), t)];
rateEquations = [k_1*A(t) == rho_1(t), k_2*B(t) == rho_2(t),...
    k_3*C(t) == rho_3(t), k_4*B(t) == rho_4(t)];
myModel = [diffEquations rateEquations];
diffVars = [A(t) B(t) C(t) D(t)];
[M, F] = massMatrixForm(myModel, diffVars)

And here's my code (MWE) of the non-working example, which throws the above-mentioned error:

% Differential Variables
syms B(t) C(t) E(t) L(t)
% Parameters and Inputs
syms nu_54 nu_64 nu_74 nu_81 nu_82 nu_83
syms k_1 k_2 k_3 k_4
syms vol q_in B_in C_in E_in L_in
% Rates (algebraic)
syms rho_1(t) rho_2(t) rho_3(t) rho_4(t)
% Differential Equations
diffEquations = [nu_81*rho_1(t) + nu_82*rho_2(t) + nu_83*rho_3(t) - rho_4(t)...
        + q_in/vol*(B_in - B(t)) == diff(B(t), t),...
      -rho_1(t) + nu_54*rho_4(t) + q_in/vol*(C_in - C(t)) == diff(C(t), t),...
	-rho_2(t) + nu_64*rho_4(t) + q_in/vol*(E_in - E(t)) == diff(E(t), t),...
	-rho_3(t) + nu_74*rho_4(t) + q_in/vol*(L_in - L(t)) == diff(L(t), t)];
% Rate Equations
rateEquations = [k_1*C(t) == rho_1(t), k_2*E(t) == rho_2(t),...
    k_3*L(t) == rho_3(t), k_4*B(t) == rho_4(t)];
% Combining everything
diffVars = [B(t) C(t) E(t) L(t)]';
myModel = [diffEquations rateEquations];
[M, F] = massMatrixForm(myModel, diffVars)