>how can i plot functions which do romberg-integrals?
You need to quote the first argument to plot2d; try this:
(%i1) h(x) := 3 * x$
(%i2) h2(x) := romberg(h(xx), xx, 0, x);
(%o2) h2(x):=ROMBERG(h(xx),xx,0,x)
(%i3) plot2d('(h2(x)), [x, 0, 10]);
In addition to the quote, notice the parens. Instead
of romberg, you might try the 'quad_qag' integration
function; try describe("quad").
Barton