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2012-05-02 16:29:53 +0100 answered a question Integrate() does not integrate

I have the Solution (partly) The function was wrong, it came up because i wrecked it with a faulty transformation.

However I was able to do the first Step of integration with the "faulty" function.

IN:

var('a b')
ftrick = -sqrt(r^2*a + b)
BItrick = integral(ftrick, (r,r1,r2))

OUT:

Is  a  positive or negative?

IN:

view('AHA!')
assume(a<0)
assume(b>0)
BItrick = integral(ftrick, (r,r1,r2))
view(BItrick)
forget()
BItrick2 = BItrick.substitute(a == -2*cos(phi)^2)
BItrick2 = BItrick2.substitute(b == 25 )
view(BItrick2)

BItrick2 =

1/4*(6*sqrt(-18*cos(phi)^2 + 25)*cos(phi)^2 +
25*sqrt(2)*sqrt(cos(phi)^2)*arcsin(3/5*sqrt(2)*sqrt(cos(phi)^2)))/cos(ph\
i)^2 - 5/4*(2*sqrt(-50*cos(phi)^2 + 25)*cos(phi)^2 +
5*sqrt(2)*sqrt(cos(phi)^2)*arcsin(sqrt(2)*sqrt(cos(phi)^2)))/cos(phi)^2

When I try to go on sage says it doent know wheather cos(phi) ist positive or negative. So i divided the integral.

forget()
assume(cos(phi) >0)
erg1 = integral(BItrick2, (phi,phi1,0.5*pi))
forget()
assume(cos(phi) <0)
erg2 = integral(BItrick2, (phi,0.5*pi,1.5*pi))
forget()
assume(cos(phi) >0)
erg3 = integral(BItrick2, (phi,1.5*pi,2*pi))
erg = erg1+erg2+erg3

Sage does calculate for 2 minutes and then it gives me the input. The system is unable to integrate.

If you have problems with Integrations try using assume() and forget()

Thank you for your Help.

2012-05-02 05:04:56 +0100 commented answer Integrate() does not integrate

numerical calculation over simsons rule may be usefull in some cases, thanks. If you want to do this in SAGE you jus need to (i think) taylor-approximate the function and have an easy life with Integration. I will remeber that when i dont need symbolics.

2012-05-02 04:00:00 +0100 commented question Integrate() does not integrate

I want to do things symbolic. When i did it in maple yesterday, it gave me nonsense. If even $$$ got Problems with such an equation, maybe it should be an feature request. Unfortuantly iam just a student of mechanical engineering, so i cant jugdge this situation. (Is it my fault or the CAS's, i suspect mine) I,however, can do it with my own sweat and tears. Thank you so far. UPDATE: Wolfram Mathematica semms to be unable to do it (at least when you go the simple way and just tell it to Integrate)

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2012-05-01 15:42:17 +0100 asked a question Integrate() does not integrate

Good Evening

When I ask sage:

var('phi r')
phi1 = 0
phi2 = 2*pi
r1 = 3
r2 = 5
fpolar = - sqrt(-2*r^2*cos(phi)^2+25)
BI = fpolar
BI= integral(BI, (phi,phi1,phi2))
BI= integral(BI, (r,r1,r2))
BI

the result is:

-integrate(integrate(sqrt(-2*r^2*cos(phi)^2 + 25), phi, 0, 2*pi), r, 3,
5)

I've found no way to make sage integrate the expresion. It repeats my input and iam not given any new information.

When i try

BI.n()

i get

ValueError: Integrand has wrong number of parameters

Same Problem with indefinite Integrals

in:

BI = fpolar
BI= integral(BI, phi)
BI

out:

-integrate(sqrt(-2*r^2*cos(phi)^2 + 25), phi)

Why? what do I need to do to get the desired output?