test gauleg.java integrate f(p)=p^2 from a=1 to b=2
calling new gaulegf(a, b, x, w, 4)
x=1.0694318442029738 1.3300094782075718 1.6699905217924282 1.9305681557970262
w=0.1739274225687238 0.3260725774312732 0.3260725774312732 0.1739274225687238
exact area=7/3
computed area = 2.333333333333319
error= -1.4654943925052066E-14