MATLAB Answers

Subs dosen't work with one argument

1 view (last 30 days)
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.

Accepted Answer

Raynier Suresh
Raynier Suresh on 16 Mar 2021
Edited: Raynier Suresh on 16 Mar 2021
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.
  2 Comments

Sign in to comment.

More Answers (1)

Raynier Suresh
Raynier Suresh on 16 Mar 2021
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
  5 Comments
Sergey Bondarenko
Sergey Bondarenko on 16 Mar 2021
Oh, I am sorry. Forgot that I used my scripts. I attached my scripts wich I used.

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!