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Re: Sometimes <space> means multiple , sometimes not

• To: mathgroup at smc.vnet.net
• Subject: [mg75361] Re: Sometimes <space> means multiple , sometimes not
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Thu, 26 Apr 2007 03:36:28 -0400 (EDT)
• References: <f0n6su$p9d$1@smc.vnet.net>

siewsk at bp.com wrote:
> As a newbie, I was taught that <space> character in Mathematica means
> multiple. But sometimes it does not.
> 
> For example:
> 
> 4<space>2  gives 8
> 
> but
> 
> -4<space>-2 does not give -8
> 
> This strange behavior can be show below
> 
> In[1]:= 4 2   (* 4<space>2 *)
> Out[1]= 8
> 
> In[2]:= 4 +2   (* 4<space>+2 *)
> Out[2]= 6
> 
> In[3]:= +4 2   (* +4<space>2 *)
> Out[3]= 8
> 
> In[4]:= +4 +2   (* +4<space>+2 *)
> Out[4]= 6
> 
> In[5]:= +4 -2  (* +4<space>-2 *)
> Out[5]= 2
> 
> In[6]:= 4 -2   (* 4<space>-2 *)
> Out[6]= 2
> 
> In[7]:= -4 -2  (* -4<space>-2 *)
> Out[7]= -6
> 
> In[8]:= -4 2  (* -4<space>2 *)
> Out[8]= -8
> 
> 
The space rules are obviously meant to mimic ordinary algebra syntax 
rules. Although it is not common to write 2<space>4 in algebra,
x y means x times y whereas x-y (with or without embedded spaces) means 
what it says.

Unlike conventional algebra, Mathematica has to cater for 
multi-character variables, so xy has a different meaning from x<space>y.

David Bailey
http://www.dbaileyconsultancy.co.uk