# NValues

• NValues[a]

• N[a] = 3;

• NValues[a]

You can assign values to NValues:

• NValues[b] := {N[b, MachinePrecision] :> 2}

• N[b]

Be sure to use SetDelayed, otherwise the left-hand side of the transformation rule will be evaluated immediately, causing the head of N to get lost. Furthermore, you have to include the precision in the rules; MachinePrecision will not be inserted automatically:

• NValues[c] := {N[c] :> 3}

• N[c]

Mathics will gracefully assign any list of rules to NValues; however, inappropriate rules will never be used:

• NValues[d] = {foo -> bar};

• NValues[d]

• N[d]