HP Forum Archive 21

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HP PRIME - What is the fastest way... Message #1 Posted by dg1969 on 19 Oct 2013, 10:02 a.m. From CAS view I want to calculate the inverse transform Laplace of a function... invlaplace(1/(1+0.2*x+x^2) for example... It's Ok I have a blablabla function of small x as a result. Good! BUT... : I need to place a big X in place of small x for future copy/paste in the symb view F1(X)=blabla of X and then plotting these... invlaplace(1/(1+0.2*x+x^2),x='X') doesn't work subst template or subst(blabala of x, 'X') doesn't work What is the fastest way... Assuming you have a long function of small x as a result in CAS view How to transfer it in F1(X)= on symb function view ? Edited: 19 Oct 2013, 10:04 a.m.

Re: HP PRIME - What is the fastest way... Message #2 Posted by Harold A Climer on 19 Oct 2013, 10:14 a.m., in response to message #1 by dg1969 Quote: From CAS view I want to calculate the inverse transform Laplace of a function... invlaplace(1/(1+0.2*x+x^2) for example... It's Ok I have a blablabla function of small x as a result. Good! BUT... : I need to place a big X in place of small x for future copy/paste in the symb view F1(X)=blabla of X and then plotting these... invlaplace(1/(1+0.2*x+x^2),x='X') doesn't work subst template or subst(blabala of x, 'X') doesn't work What is the fastest way... Assuming you have a long function of small x as a result in CAS view How to transfer it in F1(X)= on symb function view ? I think X is a system variable. See Joe Horns list of system variables on his web page or in the thread about PRIME VARIABLES

Re: HP PRIME - What is the fastest way... Message #3 Posted by Tim Wessman on 19 Oct 2013, 11:24 a.m., in response to message #1 by dg1969 Remember to quote your variable. Note that you can't do invlaplace(1/(1+0.2*x+x^2))|x='X' directly as that will evaluate to something * Dirac(x) since the substitution happens first. You need to do it as a two step. invlaplace(1/(1+0.2*x+x^2)) then <result>|x='X' As a side note, the Get from Home/CAS was supposed to do a bit of intelligent rewriting to help avoid this type of thing. It fell on the list of "get to it later" though unfortunately. :-( TW

Re: HP PRIME - What is the fastest way... Message #4 Posted by dg1969 on 19 Oct 2013, 12:06 p.m., in response to message #3 by Tim Wessman Thanks for the quality of your listening Tim, I've made a mistake in editing my post... I have first try : invlaplace(1/(1+0.2*x+x^2),x,'X') with no success... BUT then I have already try what you suggest : first command line : invlaplace(1/(1+0.2*x+x^2)) give me a first result : 1.00*SIN(0.99*x)*EXP(-0.1*x) as expected then second command line : 1.00*SIN(0.99*x)*EXP(-0.1*x)|x='X' with quotes ! And the result is : 0. !!! The same happen with subst(1.00*SIN(0.99*x)*EXP(-0.1*x),x='X') I'am in CAS view...

Re: HP PRIME - What is the fastest way... Message #5 Posted by Tim Wessman on 19 Oct 2013, 12:13 p.m., in response to message #4 by dg1969 The decimal numbers are "reals". When you do the where | it evaluates approximately since they are non-exact objects. You can either click the [a b/c] key to toggle the decimals first before the where, or start with 2/10 in the beginning and it will work. I'll investigate why a simple substitution is evaluating down. I definitely don't think that should be the case. TW

Re: HP PRIME - What is the fastest way... Message #6 Posted by dg1969 on 19 Oct 2013, 12:14 p.m., in response to message #4 by dg1969 Here is something strange for me.... In fact what you suggest, Tim, works but only if I use exact terms in the original Laplace form : first command : invlaplace(1/(1+(2/10)*x+x^2)) 2/10 in place of 0.2 !! and then ExactFirstResultOf(x)|x='X' do the job !! Can you comment these ? Thanks for your help EDIT : Tim you give the answer before I place this last post !! ;o) ! Edited: 19 Oct 2013, 12:36 p.m.

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