Strange Answer
- To: mathgroup at yoda.physics.unc.edu
- Subject: Strange Answer
- From: puglisi at settimo.italtel.it
- Date: Thu, 11 Nov 93 15:25:24 MST
---------------------------------------------
Gigi Ventura (VENTURA at pd.infn.it) noticed the following
"strange behaviour" of MMA:
In[1]:=
g1[x_]:=+x
In[2]:=
g1[2,3,4]
Out[2]=
9
In[3]:=
g2[x_]:=-x
In[4]:=
g2[2,3,4]
Out[4]=
-24
He says: the answer, that may be unexpected, is explained
by the multiplication (by-1) implicitly required in the sign
change. The priority of multiplication with respect to addition
makes the result.
To obtain the desired result parenthesis should be used:
In[5]:=
g3[x_]:=-(+x)
In[6]:=
g3[2,3,4]
Out[6]=
-9
I forward this notice, since it might interest some other user.
Giacomo Torzo
---------------------------------------------
I think the behavior you observe is wrong and due to a faulty
version of Mma.
Here is what I get:
In[5]:= $Version
Out[5]= HP 9000 Series 300 (HP-UX) 1.2 (December 13, 1990)
In[6]:= g1[x_]:=+x
In[7]:= g1[2,3,4]
Out[7]= g1[2, 3, 4]
In[8]:= g2[x_]:=-x
In[9]:= g2[2,3,4]
Out[9]= g2[2, 3, 4]
Alberto Puglisi
ITALTEL
Central Research Laboratories, DRSC-IS CLTB
20019 Castelletto di Settimo Milanese (Milano)
Italy
phone: (+39)(2)4388-8299
fax: (+39)(2)4388-7989
e-mail: puglisi at settimo.italtel.it