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MathGroup Archive 1993

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No Error in Mathematica!

  • To: mathgroup at
  • Subject: No Error in Mathematica!
  • From: puglisi at
  • Date: Mon, 8 Nov 93 16:43:25 MST

John Writes:

I just starting playing with Mathematica and I cannot seem to
 resolve the following output.
  In[1]:= x=b
  Out[1]= b
  In[2]:= x^2
  Out[2]= b^2  (* as I would expect)
  In[3]:= x^2/.x->a
  Out[3]= a^2  
  In[4]:= x=2
  Out[4]= 2
  In[5]:= x^2/.x->7  
  Out[5]= 4   

  What is going on? considering output %3 I would have thought that 
  %5 would be 49
The behavior observed is no error,it is the expected one from Mathematica.

What happens here is that x=2, and x^2/.x->7 tries to replace x with the value 7
in the constant function 2^2==4.

Another way to put it is that Mathematica does symbolic computation,
but when it sees a number understand it as a number.

Hint: Type ?x after each new input line.


Alberto Puglisi

Central Research Laboratories, DRSC-IS CLTB
20019 Castelletto di Settimo Milanese (Milano)
phone:  (+39)(2)4388-8299
fax:    (+39)(2)4388-7989
e-mail: puglisi at

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