B = value("A") is effectively the same as B = A, where A is the name of a
user-defined variable. This is useful when the name of the variable is itself
held in a string variable. See user-defined variables (p. ). It also allows you to
read the name of a variable from a data file. If the argument is a numerical
expression, value() returns the value of that expression. If the argument is a
string that does not correspond to a currently defined variable,
value() returns NaN.