On Thu, Dec 4, 2008 at 12:57 PM, Vijay <[EMAIL PROTECTED]> wrote:
>
> Hi: I am trying to evaluate a double integral (since I cannot put
> LaTeX, the 'S' below
> stands for the integral sign:)
>
> 1 sqrt(x)
> S S 4xy - y^3 dy dx
> 0 x^3
>
> This is what I put into sage:
>
> sage: var('x,y')
> (x, y)
> sage: f=4*x*y-y^3
> sage: print f
> 3
> 4 x y - y
>
> sage: print integrate(integrate(f,y,x^3,x^0.5),y,0,1)
> ---------------------------------------------------------------------------
> TypeError Traceback (most recent call
> last)
>
> /home/vkg/sage-3.1.1/<ipython console> in <module>()
>
> /home/vkg/sage-3.1.1/local/lib/python2.5/site-packages/sage/calculus/
> functional.
> py in integral(f, *args, **kwds)
> 252 """
> 253 try:
> --> 254 return f.integral(*args, **kwds)
> 255 except ValueError, err:
> 256 raise err
>
> /home/vkg/sage-3.1.1/local/lib/python2.5/site-packages/sage/calculus/
> calculus.py
> in integral(self, v, a, b)
> 2523 raise ValueError, "Integral is divergent."
> 2524 else:
> -> 2525 raise TypeError, error
> 2526
> 2527
>
> TypeError: Computation failed since Maxima requested additional
> constraints (use
> assume):
> Is x positive or negative?
>
> Am I doing something wrong here?
Use the assume command to get past this. Here's a complete session that shows
what to do:
sage: var('x,y')
sage: f=4*x*y-y^3
sage: print f
3
4 x y - y
sage: print integrate(integrate(f,y,x^3,x^0.5),y,0,1)
boom
sage: forget(); assume(x>0)
sage: print integrate(integrate(f,y,x^3,x^0.5),y,0,1)
12 7 2.0 2
x - 8 x x - 8 x
---------- - -----------
4 4
sage: forget(); assume(x<0)
sage: print integrate(integrate(f,y,x^3,x^0.5),y,0,1)
Traceback (most recent call last):
...
TypeError: Error executing code in Maxima
Do you think it would be better if instead of
sage: print integrate(integrate(f,y,x^3,x^0.5),y,0,1)
... Is x positive or negative?
one saw:
... Is x positive or negative? (Try using the assume command.)
William
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