# [✓] Evaluate this constant expression?

Posted 10 months ago
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 Is this a bug or a feature? I can't figure out how to get Mathematica to evaluate this constant expression, Out[16]. If I apply N[ ] to it, it stays the same (Out[17]). Strangely, though, if I paste the same expression manually into a new line, In[18], it evaluates fine. Why? (I'm using Mathematica 10.3.1 for Linux x86.) In[16]:= wHexToDec["3FFBB67AE8584CAA"] Out[16]= + 2^(0) + 2^(-1) + 2^(-3) + 2^(-4) + 2^(-5) + 2^(-7) + 2^(-8) +\ > 2^(-10) + 2^(-11) + 2^(-14) + 2^(-15) + 2^(-16) + 2^(-17) + 2^(-19) +\ > 2^(-21) + 2^(-22) + 2^(-23) + 2^(-25) + 2^(-30) + 2^(-32) + 2^(-33) +\ > 2^(-38) + 2^(-41) + 2^(-42) + 2^(-45) + 2^(-47) + 2^(-49) + 2^(-51) In[17]:= N[In[16]] Out[17]= + 2^(0) + 2^(-1) + 2^(-3) + 2^(-4) + 2^(-5) + 2^(-7) + 2^(-8) +\ > 2^(-10) + 2^(-11) + 2^(-14) + 2^(-15) + 2^(-16) + 2^(-17) + 2^(-19) +\ > 2^(-21) + 2^(-22) + 2^(-23) + 2^(-25) + 2^(-30) + 2^(-32) + 2^(-33) +\ > 2^(-38) + 2^(-41) + 2^(-42) + 2^(-45) + 2^(-47) + 2^(-49) + 2^(-51) In[18]:= + 2^(0) + 2^(-1) + 2^(-3) + 2^(-4) + 2^(-5) + 2^(-7) + 2^(-8) +\ 2^(-10) + 2^(-11) + 2^(-14) + 2^(-15) + 2^(-16) + 2^(-17) + 2^(-19) +\ 2^(-21) + 2^(-22) + 2^(-23) + 2^(-25) + 2^(-30) + 2^(-32) + 2^(-33) +\ 2^(-38) + 2^(-41) + 2^(-42) + 2^(-45) + 2^(-47) + 2^(-49) + 2^(-51) 3900231685776981 Out[18]= ---------------- 2251799813685248 In[19]:= N[Out[18]] Out[19]= 1.73205 
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Posted 10 months ago
 Take a look at FullForm[wHexToDec[...]].I wouldn't be surprised if it is, say a string, and of course N will leave strings unchanged.
Posted 10 months ago
 Thanks, Ilian. You hit the nail on the head! n[23]:= FullForm[wHexToDec["3FFBB67AE8584CAA"]] Out[23]//FullForm= "+ 2^(0) + 2^(-1) + 2^(-3) + 2^(-4) + 2^(-5) + 2^(-7) +\ > 2^(-8) + 2^(-10) + 2^(-11) + 2^(-14) + 2^(-15) + 2^(-16) + 2^(-17) +\ > 2^(-19) + 2^(-21) + 2^(-22) + 2^(-23) + 2^(-25) + 2^(-30) + 2^(-32) +\ > 2^(-33) + 2^(-38) + 2^(-41) + 2^(-42) + 2^(-45) + 2^(-47) + 2^(-49) +\ > 2^(-51)" If I apply ToExpression[ ] to it, I get what I wanted... In[24]:= ToExpression[wHexToDec["3FFBB67AE8584CAA"]] 3900231685776981 Out[24]= ---------------- 2251799813685248 Problem solved, thanks again!
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