CAS laplace transform w/ undefined function

09132018, 04:35 AM
Post: #1




CAS laplace transform w/ undefined function
Hi all,
Working through my circuit book (Thomas & Rosa 2001), we are taking laplace transforms of undefined functions. For example: L(dv(t)/dt + 6v(t)) = sV(s) + v(0) +6V(s) How would I do this HP Prime / xcas? I would be happy with a link if there is one, but I have searched the docs as best I could. As you can probably guess, we then solve for V(s) = .... and take the inverse transform, but that isn't the part where I am stuck currently. ( And forgive me if I got the above transform wrong, I am sure it is close and conveys the idea...) Thanks! 

09132018, 05:47 AM
Post: #2




RE: CAS laplace transform w/ undefined function
There is nothing builtin to handle unassigned function. If you want to check integration by part, you can run ibpu(exp(s*x)*diff(f(x),x),exp(s*x))


09142018, 04:48 AM
Post: #3




RE: CAS laplace transform w/ undefined function
Do you or anyone have advice on how to use the laplace() transform function to solve a differential like the following?
dv(t)/dt + 6v(t) = sin(t) In the book you take laplace transforms of each side, solve for V(s), but I don't see how to do that in xcas. (Not sure why you suggested integration by parts, but it is highly likely I missed something.) Thanks! 

09142018, 06:55 AM
(This post was last modified: 09142018 06:56 AM by parisse.)
Post: #4




RE: CAS laplace transform w/ undefined function
Replace v(0) by it's value, solve for V(s)
y:=laplace(sin(t),t,s); [vsol]:=solve(s*vs + v0 +6vs=y,vs); ilaplace(vsol,s,t); Check with desolve: desolve([v' + 6v = sin(t) ,v(0)=v0],t,v) 

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