I saw under http://docs.sympy.org/dev/tutorial/simplification.html#powsimp 
that it is impossible to combine radicals using powersimp:

"This means that it will be impossible to undo this identity with powsimp(), 
because even if powsimp() were to put the bases together, they would be 
automatically split apart again."

I was wondering if it was possible to do this any other way. 

For a toy example I have 

        import sympy
        L = sympy.symbols('L', real=True, finite=True, positive=True)
        sympy.sqrt(L) * sympy.sqrt(pi)

and I would like to have it return sympy.sqrt(L * pi)
Is there any way to do this?

What I'd really like is if it combined these terms in this real example: 

        import simplify
        import vtool as vt
        import sympy
        sigma, dist, L = sympy.symbols('sigma, distij, L', real=True, 
finite=True, positive=True)
        kernel = (1 / sympy.sqrt(sigma ** 2 * 2 * sympy.pi)) * 
sympy.exp((-dist ** 2) / (2 * sigma ** 2))
        phi = (1 / L) * kernel
        logphi = sympy.simplify(sympy.log(phi))
        logphi = sympy.logcombine(logphi)

So I would get 
-distij**2/(2*sigma**2) - log(sqrt(2 * pi)*L*sigma)

instead of 

-distij**2/(2*sigma**2) - log(sqrt(2)*sqrt(pi)*L*sigma)



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