Simplifiy function incorrect result?

Hello,

I ran into a problem using Matlab simplify function. I have the following code:

syms q1 q2 q3 real

syms l3 l4 real

Ja = [-sin(q1)*(l3*cos(q2)+l4*cos(q2+q3)), -cos(q1)*(l3*sin(q2)+l4*sin(q2+q3)), -l4*cos(q1)*sin(q2+q3)

cos(q1)*(l3*cos(q2)+l4*cos(q2+q3)), -sin(q1)*(l3*sin(q2)+l4*sin(q2+q3)), -l4*sin(q1)*sin(q2+q3)

0, -l3*cos(q2)-l4*cos(q2+q3), -l4*cos(q2+q3)];

detJa = det(Ja);

simplify(detJa)

this code returns:

l3*l4*(l3*cos(q2)*sin(q3) - l4*sin(q2) + l4*cos(q3)^2*sin(q2) + l4*cos(q2)*cos(q3)*sin(q3))

If I calculate this by hand, I get the following result:

l3*l4*sin(q3)*(l3*cos(q2)+l4*cos(q2+q3))

I am pretty sure that this is the correct answer, but why does simplifiy return a different result?

Thanks in advance for any help

Answer 1

[Star Strider]

You just need to tell simplify to keep simplifying:

DetJa = simplify(detJa, 'Steps',500)

producing:

DetJa = 
l3*l4*sin(q3)*(l4*cos(q2 + q3) + l3*cos(q2))

Answer 2

[Aston Martin]

Thanks a lot! :)

[Star Strider]

As always, my pleasure!