Subs dosen't work with one argument

I want to use subs to subsistute some constants in my equations, but I get error when I try to do it.

There is code of my calculation:

clc;
clear;
clearvars;
syms X(t) Y(t) alpha(t) beta(t) theta(t);
syms phi(t) [2 2];
syms chi m_0 g M_z s_0 gamma_0 J_t_0 J_p_0 real;
syms c l [1 3] real;
syms h r J_t J_p s gamma m M [1 2] real;
syms R_Et R_E [3 2];
syms R_Bt R_B [3 4];
syms J_E [3 3 2]
syms d [1 5] real;
syms R_G [3 1];
J_G = diag([J_t_0, J_t_0, J_p_0]);
J_E(:,:,1) = diag([J_t1, J_t1, J_p1]);
J_E(:,:,2) = diag([J_t2, J_t2, J_p2]);
R_C = [X;Y;0];
R_Gt = [s_0*cos(gamma_0);s_0*sin(gamma_0);0];
R_Bt(:,1) = [r1*cos(phi1_1);r1*sin(phi1_1);0];
R_Bt(:,2) = [r1*cos(phi2_1);r1*sin(phi2_1);0];
R_Bt(:,3) = [r2*cos(phi1_2);r2*sin(phi1_2);0];
R_Bt(:,4) = [r2*cos(phi2_2);r2*sin(phi2_2);0];
R_Et(:,1) = [s1*cos(gamma1);s1*sin(gamma1);h1];
R_Et(:,2) = [s2*cos(gamma2);s2*sin(gamma2);h2];

P_alpha = [[1 0 0];
    [0 cos(alpha) sin(alpha)];
    [0 -sin(alpha) cos(alpha)]];
P_beta = [[cos(beta) 0 -sin(beta)];
    [0 1 0];
    [sin(beta) 0 cos(beta)]];
P_theta = [[cos(theta) sin(theta) 0];
    [-sin(theta) cos(theta) 0];
    [0 0 1]];
A = P_theta*P_beta*P_alpha;
for_assume = [alpha, beta];
for_assume = transpose(symToVector(for_assume, 2));
A = assumeSmallTrig(A, for_assume);
A = assumeSmall(A,for_assume, 0);

P_chi = [[cos(chi) 0 -sin(chi)];%why???????
    [0 1 0];
    [sin(chi) 0 cos(chi)]];
Omega = P_chi*(P_theta*P_beta*[diff(alpha);0;0] + ...
    P_theta*[0;diff(beta);0] + [0;0;diff(theta)]);
for_assume = [alpha, beta, chi];
for_assume = transpose(symToVector(for_assume, 3));
Omega = assumeSmallTrig(Omega, for_assume);

R_G = R_C + transpose(A)*R_Gt;
R_G = simplify(R_G, "Steps",30);
for j = 1:2
    R_E(:,j) = R_C + transpose(A)*R_Et(:,j);
    R_E(:,j) = simplify(R_E(:,j), "Steps",30);
end
for j = 1:2
    R_B(:,j) = R_E(:,1) + transpose(A)*R_Bt(:,j);
    R_B(:,j+2) = R_E(:,2) + transpose(A)*R_Bt(:,j+2);
    R_B(:,j) = simplify(R_B(:,j), "Steps",30);
    R_B(:,j+2) = simplify(R_B(:,j+2), "Steps",30);
end

v_r = symToVector(diff(R_G, 't'),3);
syms T V D;
T = 0; V =0; D = 0;
temp = [phi1_1(t), phi2_1(t), phi1_2(t), phi2_2(t)];
for j = 1:2
    v_o = diff(R_E(:,j), 't');
    v_b_1 = diff(R_B(:,j), 't');
    v_b_2 = diff(R_B(:,j+2), 't');
    T = T + M(j)*(v_o(1)^2+v_o(2)^2) + transpose(Omega)*(J_E(:,:,j)*Omega) + ...
        m(1)*(v_b_1(1)^2+v_b_1(2)^2) + m(2)*(v_b_2(1)^2+v_b_2(2)^2);
    V = V + M(j)*g*R_E(1,j) + m(1)*g*R_B(1,j) + m(2)*g*R_B(1,j+2);
    D = D + d4/2*diff(temp(j))^2 + d5/2*diff(temp(j+2))^2;
end
T = T/2 + 1/2*(m_0*(v_r(1)^2+v_r(2)^2)+transpose(Omega)*(J_G*Omega));
R_G = symToVector(R_G,3);
V = V + c1/2*((X-l1*beta)^2+(Y+l1*alpha)^2)+...
    c2/2*((X+l2*beta)^2+(Y-l2*alpha)^2) + m_0*g*R_G(1);
D = D + d1/2*((diff(X)-l1*diff(beta))^2+(diff(Y)+l1*diff(alpha))^2)+...
    d2/2*((diff(X)+l2*diff(beta))^2+(diff(Y)-l2*diff(alpha))^2)+...
    d3/2*(diff(theta)^2);
L = T - V;

Lagr = sym(zeros(9,1));
Lagr_r = [0; 0; M_z*beta; 0; M_z; 0; 0; 0; 0];
Lagr_r = symToVector(Lagr_r, 9);
temp_1 = [X(t), Y(t), alpha(t), beta(t), theta(t), ...
    phi1_1(t), phi2_1(t), phi1_2(t), phi2_2(t)];
for_assume = [alpha, beta, chi];
for_assume = transpose(symToVector(for_assume, 3));
for i = 1:9
    Lagr(i) = diff(diff(L,diff(temp_1(i),t)),t) - diff(L,temp_1(i)) + diff(D,diff(temp_1(i),t));
    Lagr(i) = assumeSmall(Lagr(i),for_assume,2);
end
Lagr = simplify(Lagr);
Lagr = Lagr - Lagr_r;

s_0 = 0.01; gamma_0 = 0.01; chi = 0.02; s1 = 0.001;
s2 = 0.001; gamma1 = 1; gamma2 = 1+pi/2; m_0 = 10; l0 = 1;
r1 = l0/10; r2 = l0/10;
l1 = 0.5; l2 = l0-l1; J_p_0 = m_0*(r2)^2/8; 
J_t_0 = J_p/2 + m_0*l0^2/12; m1=0.375;m2 = 0.375;
d1 = 100; d2 = 100; d3 = 2; d4 = 10; d5= 10;
h1 = 0.45; h2 = -0.45; c1 = 2*10^5; c2 = 2*10^5;
M_z = 2000; omega = 600; g = 9.81;
J_p1 = m1*(r1)^2/8; J_t1 = J_p1/2; M1 = 0.5;
J_p2 = m2*(r2)^2/8; J_t2 = J_p2/2; M2 = 0.5;
lagr_subs = subs(Lagr);

Error ocurs in last string. It is:

Error using mupadengine/feval_internal
Two arguments expected.

Error in sym/subs (line 93)
            X{k} = symfun(feval_internal(symengine,X{k},args_c{:}),args);

I don't understand how to fix it. If somebody have sugestions or had that trouble before, please give me advice.

Answer 1

[Raynier Suresh]

Hi,The error is due to the symbolic variable beta(t), beta is an inbuilt function with two arguments. To understand this try the below code

%% No Error Will occur
syms Beta(t)
subs(Beta)

%% Because of conflict with an internal function error will occur
syms beta(t)
subs(beta)

To avoid this use a different name for beta variable. Your code works fine once the beta is renamed.

[Sergey Bondarenko]

Thank you for helping me. Yes, now my code works without errors.

[Walter Roberson]

Nice catch!

Answer 2

[Raynier Suresh]

Hi, To use subs with one argument you must assign values to the symbolic variable before using the subs command. For more information refer the below example

https://www.mathworks.com/help/symbolic/subs.html#btqh7su-1

[Sergey Bondarenko]

Hi, How you could see, I done it in this way. Before using subs I assign constants. Here it is:

...

s_0 = 0.01; gamma_0 = 0.01; chi = 0.02; s1 = 0.001;
s2 = 0.001; gamma1 = 1; gamma2 = 1+pi/2; m_0 = 10; l0 = 1;
r1 = l0/10; r2 = l0/10;
l1 = 0.5; l2 = l0-l1; J_p_0 = m_0*(r2)^2/8; 
J_t_0 = J_p/2 + m_0*l0^2/12; m1=0.375;m2 = 0.375;
d1 = 100; d2 = 100; d3 = 2; d4 = 10; d5= 10;
h1 = 0.45; h2 = -0.45; c1 = 2*10^5; c2 = 2*10^5;
M_z = 2000; omega = 600; g = 9.81;
J_p1 = m1*(r1)^2/8; J_t1 = J_p1/2; M1 = 0.5;
J_p2 = m2*(r2)^2/8; J_t2 = J_p2/2; M2 = 0.5;

lagr_subs = subs(Lagr);

[Raynier Suresh]

If you can tell which MATLAB version you are using it will be helpful for further investigation, you can use the ver command to get this.

[Sergey Bondarenko]

I am using MATLAB Version: 9.9.0.1467703 (R2020b).

[Raynier Suresh]

I am currently unable to reproduce this because of the "symToVector" in your code, Will you be able to provide this function?. It will be better if you can share all the necessary files.

[Sergey Bondarenko]

Oh, I am sorry. Forgot that I used my scripts. I attached my scripts wich I used.