Returns the expected real value of node, based on the current beliefs for node, and if std_dev is non-NULL, *std_dev will be set to the standard deviation. Returns UNDEF_DBL if the expected value couldn't be calculated.

Pass NULL (i.e., 0) for arguments x3 and x4; they are there for future expansion.

node must be continuous discretized, or must be discrete with a levels list defined to supply real values.

For continuous discretized nodes it assumes the belief for each state is distributed evenly over each discretized interval. Because of that, it can't handle infinite tails (returns UNDEF_DBL).

This function is not for expected utility; for that see GetNodeExpectedUtils_bn.