Compute pdf maximum

Dear expert, can you suggest me a way to find the maximum of a pdf. For example for a normal distribution I would like to find 1/sqrt(2 pi) = 0.4.

Declare the objects:

import ROOT
x = ROOT.RooRealVar('x', 'x', -10, 10)
mean = ROOT.RooRealVar('mean', 'mean', 1, -10, 10)
sigma = ROOT.RooRealVar('sigma', 'sigma', 1, 0.1, 1)
gaus = ROOT.RooGaussian("gaus", "gaus", x, mean, sigma)

these methods seems not to work, they always return 0

print gaus.getMaxVal(ROOT.RooArgSet(mean,sigma))
print [gaus.maxVal(i) for i in range(10)]
print gaus.maxVal(gaus.getMaxVal(ROOT.RooArgSet(x, mean, sigma)))

if I convert the function to a TF1 its maximum is at 1:

f = gaus.asTF(ROOT.RooArgList(x))
print f.GetMaximum(-10, 10), f.GetMaximumX(-10, 10), f.Eval(2.2)