MATLAB: Partfrac() function returning same expression that was given as input

MATLABpartfrac

I have the following expression:
(4*l^2*m5 – 2*dl^2*m5*cos(2*THETA1(t) – 4*THETA2(t) + 4*THETA3(t) – 4*THETA4(t) + 2*THETA5(t)))/(12*dl^2)
I want the denominator (i.e. 12*dl^2) to be divided across all the numerator terms so that the resulting expression is the sum of a bunch of terms.
partfrac((4*l^2*m5 - 2*dl^2*m5*cos(2*THETA1(t) - 4*THETA2(t) + 4*THETA3(t) - 4*THETA4(t) + 2*THETA5(t)))/(12*dl^2))
ans =
 
(- m5*cos(2*THETA1(t) - 4*THETA2(t) + 4*THETA3(t) - 4*THETA4(t) + 2*THETA5(t))*dl^2 + 2*m5*l^2)/(6*dl^2)
When I use the partfrac() function in MATLAB to do this, it gives me almost the same expression again.
Please help.

Best Answer

The partfrac function needs more information, specifically the variable (not expression) that you want it to use.
This (note that I provided the variable ‘dl’ and a useful name-value pair): 
syms dl l m5 t THETA1(t) THETA2(t) THETA3(t) THETA4(t) THETA5(t) 
Eq = (4*l^2*m5 - 2*dl^2*m5*cos(2*THETA1(t) - 4*THETA2(t) + 4*THETA3(t) - 4*THETA4(t) + 2*THETA5(t)))/(12*dl^2);
Eq_pf = partfrac(Eq, dl, 'FactorMode','full')
produces: 
Eq_pf =
(l^2*m5)/(3*dl^2) - (m5*cos(2*THETA1(t) - 4*THETA2(t) + 4*THETA3(t) - 4*THETA4(t) + 2*THETA5(t)))/6
That is as much as it can do.
.
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