partial fractions and complex roots in 50g

Hello,

Doing partial fractions with this in the denominator: s^2+10s+169

gives me a crazy result. When I simply factor this, I know why. I get

something involving e^i*ATAN(12/5) etc. All I really want is (s+5-12i)

(s+5+12j).

I played with most of the simplification functions in the ALG and

EXP&LN menus, but none really makes a difference.

I know it's not too hard to do by hand, but that's not why I have this

calculator.

Ultimately I want to get the partial fractions with an expression like

that in the denominator, which I then take the inverse Laplace

transform of. It works great with real roots, just not with complex

roots.

Any ideas?

Thanks!

Christoph

Re: partial fractions and complex roots in 50g

On 16 Okt., 17:46, Christoph Koehler <christoph.koeh...@gmail.com>

wrote:

[color=blue]

> Doing partial fractions with this in the denominator: s^2+10s+169

> gives me a crazy result. When I simply factor this, I know why.[/color]

On my 50g it works like this

Choose MODE CAS and check the flag for Complex, OK

Then type enter x^2+10*x+169 and choose EDIT and FACTO

and you get the result, you want

Regards,

Peter

Re: partial fractions and complex roots in 50g

If you try it with RECT (rectangular coordinates) mode and Complex

mode both turned on, I think it will do what you want. Having the

coordinates in Polar or Spherical modes causes some complex

expressions to be displayed in polar form, r*exp(i*theta), instead of

rectangular form, a+bi. I've noticed this mode setting also affects

certain integrals.

-wes

On Oct 16, 6:46*pm, Christoph Koehler <christoph.koeh...@gmail.com>

wrote:[color=blue]

> Hello,

>

> Doing partial fractions with this in the denominator: s^2+10s+169

> gives me a crazy result. When I simply factor this, I know why. I get

> something involving e^i*ATAN(12/5) etc. All I really want is (s+5-12i)

> (s+5+12j).

> I played with most of the simplification functions in the ALG and

> EXP&LN menus, but none really makes a difference.

> I know it's not too hard to do by hand, but that's not why I have this

> calculator.

>

> Ultimately I want to get the partial fractions with an expression like

> that in the denominator, which I then take the inverse Laplace

> transform of. It works great with real roots, just not with complex

> roots.

>

> Any ideas?

>

> Thanks!

>

> Christoph[/color]

Re: partial fractions and complex roots in 50g

On Oct 16, 12:10*pm, Wes <wjltemp...@yahoo.com> wrote:[color=blue]

> If you try it with RECT (rectangular coordinates) mode and Complex

> mode both turned on, I think it will do what you want. *Having the

> coordinates in Polar or Spherical modes causes some complex

> expressions to be displayed in polar form, r*exp(i*theta), instead of

> rectangular form, a+bi. *I've noticed this mode setting also affects

> certain integrals.[/color]

I am so glad you figured that out. That was exactly it, and it makes a

lot of sense.

Thanks again!

Christoph

Re: partial fractions and complex roots in 50g

On Thu, 16 Oct 2008 10:10:43 -0700 (PDT), Wes <wjltemp-gg@yahoo.com>

wrote:

[color=blue]

>If you try it with RECT (rectangular coordinates) mode and Complex

>mode both turned on, I think it will do what you want. Having the

>coordinates in Polar or Spherical modes causes some complex

>expressions to be displayed in polar form, r*exp(i*theta), instead of

>rectangular form, a+bi. I've noticed this mode setting also affects

>certain integrals.

>[/color]

Could you please point me to ANY HP50 manual where the above procedure

is described?

A.L.

Re: partial fractions and complex roots in 50g

No problems on the 50g turn the calculator on clear all entries enter equation in frequency domain then white left arrow key then (1) and selection 2 Polynomial and then 15 Partfrac and then if you just want to find the inverse laplace follow below.

clear all entries on screen go into CALC menu by pressing white left arrow then key (4) select 3 Differential equations then 2 ILAP and enter the equation in the frequency domain f(s) to get f(t) as the answer. To do it manually eg to find the inverse laplace 1/(s^2+s+1) it needs the form As+B/(s^2+s+1). Then

1/(s^2+s+1)=As+B/(s^2+s+1) therefore 1=As+B when A=0; B=1

(0(s+0.5)/(s+0.5)^2+0.75)+(1/(s+0.5)^2+0.75) the denominators in perfect squares

From the inverse laplace transform tables you may derive that the solution is

(0e^(-0.5t))*cos(((0.75)^0.5)t)+(1/(0.75)^0.5)(e^(-0.5t))*sin(((0.75)^0.5)t)

I believe this to be correct