today              max |F - dphi/dr| / max F = 1.1e-04
plummer            max |F - dphi/dr| / max F = 1.9e-07
logratio L=800     max |F - dphi/dr| / max F = 1.9e-07
splummer lam=800   max |F - dphi/dr| / max F = 1.2e-05
lamb               max |F - dphi/dr| / max F = 5.0e-06
lamb+halo L=800    max |F - dphi/dr| / max F = 5.1e-06
conserve L=800     max |F - dphi/dr| / max F = 1.9e-07
Ein shader form vs mpmath: max abs err 2.3e-07
