The following error occurred converting from sym to double: Unable to convert expression containing symbolic variables into double array..

I'm solving the problem with a long formula. There is no problem with other parts, but it seems that the problem occurs in the above code. How can I solve this problem? The problem continues to occur even after using 'subs'

can anyone help me please.....?

ERROR

symengine

Unable to convert expression containing symbolic variables into double array. Apply 'subs'

function first to substitute values for variables.

l1= 50; 
l2= 50;
l3= 10;

x2 = l1*cos(theta1);

Unrecognized function or variable 'theta1'.

x3 = l2*cos(theta1+theta2)+ x2;
y2 = l1*sin(theta1);
y3 = l2*sin(theta1+theta2)+ y2;

a = acosd((l1^2 + l2^2 - (sqrt(x3^2 + y3^2))^2 )/(2*l1*l2));
B = acosd((l1^2 + (sqrt(x3^2 + y3^2))^2 - l2^2 )/(2*l1*(sqrt(x3^2 + y3^2))));

theta1 = atan2d(y3,x3)+B;
theta2 = -(180-a);
theta3 = - theta1 - theta2;

for i=[1:100]
    k=dt*i;
    th1(i)=double(subs(theta1,t,k));   % error point
    th2(i)=double(subs(theta2,t,k));
    th3(i)=double(subs(theta3,t,k));
end

t=[0.01:0.1:10];
figure(1)

hold on
plot(t,th1);
plot(t,th2);
plot(t,th3);
title('theta')
legend('theta1','theta2','theta3')
hold off

[Walter Roberson]

x2 = l1*cos(theta1);

theta1 is not defined

x3 = l2*cos(theta1+theta2)+ x2;

You use theta1 to define x3 and other variables

theta1 = atan2d(y3,x3)+B;

If theta1 exists, then you overwrite theta1 with a new value (if it does not exist, you would not have gotten this far.)

If you are trying to define a balance equation, with x2, x3, y3 being defined in theta1 and simultaneously theta1 must have that particular value in terms of variables defined by theta1, then you need to create an equation, like

eqn = theta1 == atan2d(y3, x3) + B

and solve the eqn

Answer 1

[VBBV]

syms theta1 theta2 
t=[0.01:0.1:10];
l1= 50; 
l2= 50;
l3= 10;
dt = 1;
x2 = l1*cos(theta1)

x2 = 

x3 = l2*cos(theta1+theta2)+ x2;
y2 = l1*sin(theta1);
y3 = l2*sin(theta1+theta2)+ y2;
a = acosd((l1^2 + l2^2 - (sqrt(x3^2 + y3^2))^2 )/(2*l1*l2));
B = acosd((l1^2 + (sqrt(x3^2 + y3^2))^2 - l2^2 )/(2*l1*(sqrt(x3^2 + y3^2))));
t1 = atan2d(y3,x3)+B;
t2 = -(180-a);
t3 = - theta1 - theta2;
for i=[1:100]
    k=dt*i;
    y1 = subs(t1,{theta1,theta2},{k,k});
    y2 = subs(t2,{theta1,theta2},{k,k});
    y3 = subs(t3,{theta1,theta2},{k,k});
    th1(i)=double(y1);   % error point
    th2(i)=double(y2);
    th3(i)=double(y3);
end

figure(1)
hold on
plot(t,th1);
plot(t,th2);
plot(t,th3);
title('theta')
legend('theta1','theta2','theta3')
hold off

[VBBV]

In the below lines, theta1 expression includes both symbolic variables, theta1 and theta2, and its not given a numeric substitution, so it gives error

  th1(i)=double(subs(theta1,t,k));   % error point
  th2(i)=double(subs(theta2,t,k));
  th3(i)=double(subs(theta3,t,k));