Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

% DH parameters using symbolic tool box 
clear 
clc
%% 
syms theta1 theta2 theta3

R1 = [ cos(theta1),      0,  sin(theta1), 0;
       sin(theta1),      0, -cos(theta1), 0;
                 0,      1,           0, 0;
                 0,       0,          0, 1];

R2 =[ cos(theta2), -sin(theta2),      0, 0.1*cos(theta2);
      sin(theta2),  cos(theta2),      0, 0.1*sin(theta2);
               0,             0,      1,             0;
               0,             0,      0,             1];
 
R3 =[ cos(theta3),      0,  sin(theta3), 0;
      sin(theta3),      0, -cos(theta3), 0;
                0,      1,            0, 0;
                0,      0,            0, 1];

% Total Forward Matrix 
A_03 = simplify(R1 * R2 * R3);
A_13 = R2 * R3;

%% inverse kinematic 
Px = -0.135;
Py = -0.000;
Pz = -0.128;

A_03_ = A_03;

A_03_(1:3,4) = [Px Py Pz];

A_13_ = simplify(R1 \ A_03_);
A_23_ = simplify(R2 \ A_13_);
I = simplify(R3 \ A_23_);

%%
eq(1) = Px == A_03(1,4);
eq(2) = Py == A_03(2,4);
eq(3) = Pz == A_03(3,4);
eq(4) = A_13_(1,4) - R1(1,4) == 0 ;
eq(5) = A_13_(2,4) - R1(2,4) == 0 ;
eq(6) = A_13_(3,4) - R1(3,4) == 0 ;
eq(7) = A_23_(1,4) - R2(1,4) == 0 ;
eq(8) = A_23_(2,4) - R2(2,4) == 0 ;
eq(9) = A_23_(3,4) - R2(3,4) == 0 ;
eq(10) = I(1,4) == 0;
eq(11) = I(2,4) == 0;
eq(12) = I(3,4) == 0;
sol = solve(eq);

q(1:4,1) = double(sol.theta1);
q(1:4,2) = double(sol.theta2);
q(1:4,3) = double(sol.theta3);

I dont know why it keep sending me an error

Error in Inverse_kinematic (line 58)
q(1:4,1) = double(sol.theta1);

How should i change this:

sol = 
  struct with fields:
    theta1: [0×1 sym]
    theta2: [0×1 sym]
    theta3: [0×1 sym]

[Star Strider]

The reason is that it cannot solve your system:

sol = 

  struct with fields:

    theta1: [0×1 sym]
    theta2: [0×1 sym]
    theta3: [0×1 sym]

[AOF]

how should i change it ?

because in the work space it show me 1x1 sym

i am really confused

How to solve this problem ?

Answer 1

[Devineni Aslesha]

The reason for showing 1x1 sym for theta1 is that they are declared as symbolic variables using syms theta1. However, 0x1 sym is for struct sol fields theta1,theta2 and theta3 as it cannot solve your system.

For more information, rfer the following link

https://www.mathworks.com/help/symbolic/equation-solving.html