Mupad, Symbolic Ilaplace, "High" order transfer function to time domain

Iam trying to get the same plot of the step response as you would get using matlab/simulink. But i want a symbolic solution solution correct for all of the variables.

I am stuck at the last step. I'm guessing my problem has something to do with range.

Using Mupad.

Open Loop plant ol := 1/(m*s^2+b*s+k)

Proportional integral controler K := 1*(1+0.5*1/s)

Cloosed loop system cl := K*ol/(K*ol+1)

Step intput U := 1/s

Apply Step input sdomain := U*cl

Convert s to t domain tdomain := ilaplace(sdomain,s,t) Error: The second argument must be a range specification, such as 'k=a..b' or 'x in RootOf(...)'. [numeric::sum]

[Deepak Ramaswamy]

Update: My attachments are not going through. so I've just C&P the MuPAD code below:

reset()

ol := 1/(m*s^2+b*s+k)

Note: 0.5 converted to 1/2 below to keep calculations symbolic

K := 1*(1+1/2*1/s)

cl := simplify(K*ol/(K*ol+1))

U := 1/s

sdomain := U*cl

tdomain := simplify(ilaplace(sdomain,s,t))

float(tdomain | b=1 | m = 1 | k = 1)

Original: Not sure if this helps: See attached file. I converted '0.5' to a rational form to make sure you're performing symbolic calculations and for specific parameter values, you can extract an expression