simplify works differently on a variable having symbolic expression and on an absolute symbolic expression.

x =
0.5000*a3*sin(q2 - q1 + q3) - 0.5000*a2*sin(q1 + q2) - 0.5000*a2*sin(q1 - q2) - 0.5000*a3*sin(q1 + q2 + q3)
x=simplify(x)

This gives the output as

x =
0.5000*a3*sin(q2 - q1 + q3) - 0.5000*a2*sin(q1 + q2) - 0.5000*a2*sin(q1 - q2) - 0.5000*a3*sin(q1 + q2 + q3)

But when you simplify the expression as

x=simplify(0.5000*a3*sin(q2 - q1 + q3) - 0.5000*a2*sin(q1 + q2) - 0.5000*a2*sin(q1 - q2) - 0.5000*a3*sin(q1 + q2 + q3))

The output is

x =
-sin(q1)*(a3*cos(q2 + q3) + a2*cos(q2))

How can I get the latter simplification using a variable?

Answer 1

[Walter Roberson]

syms q1 q2 q3 a1 a2 a3
half = sym('0.5000');
x = half*a3*sin(q2 - q1 + q3) - half*a2*sin(q1 + q2) - half*a2*sin(q1 - q2) - half*a3*sin(q1 + q2 + q3)
x = simplify(x)

gives the same expression as you are looking for.

How exactly are you getting the 0.5000 in the symbolic expressions? I suspect that those are not exactly 0.5000, that instead you are showing the vpa() output of expressions involving constants that are close to 1/2

[Malay Tushar Nagda]

Matrix operations involving both numerical and symbolic values is the reason for 0.5000 in symbolic expression.

I ended up using entirely different solution for my university project of making a GUI based robotics toolbox.Thank you for your response and sorry for delayed reply.