A tiny type conversion problem

I'm a bit embarrassed not to be able to work this out for myself, but,
anyway...  Now that I've discovered the joys of the NumericalQuadrature
package, I want to use it to calculate the total variation of some
functions; the total variation being defined (for differentiable functions)
as the integral of the absolute value of the derivative.  So I'd like to use
something like

romberg(x+->abs(D(x/(x^3+1),x)),0.0,1.0,0.1,0.1,10,10)

But this doesn't work.  Romberg requires an anonymous function float ->
float, but the use of D returns an expression. (Expression integer, in this
example).  How, and where, do I place the type conversions so that romberg
will do its job?

Thanks,
Alasdair

-- 
Blog: http://amca01.wordpress.com

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