Query regarding Function

[Rahul Chakraborty]

Dear all,

Case1: In the following code

Clear[f,x,y]
g=Function[{x,y},x^2+2xy][b,a]

The output is found to be b^2+2 xy

Case2: But for the code

Clear[f,x,y]
g=Function[{x,y},x^2+2y][b,a]

The output is 2 a+b^2

Hence my query is why in case 1 x*y is not replaced by b and a whereas in case 2 it got replaced ?

Regards,
rc

[Oliver Roese]

"xy" is parsed as a single symbol in the former case. Try to put a space
between both variables:
Clear[f, x, y]
g = Function[{x, y}, x^2 + 2 x y][b, a]
My output is: 2 a b + b^2

Best regards
Oliver

[David Bailey]

[This thread is now closed. There have been enough answers. - Moderator]

Variable names in Mathemnatica can be more than one character long -
remember that computer algebra can require a lot of variables! Thus xy
is a quite distinct variable - space the two characters out to get a
product: x y .

Note that it is always useful to examine dubious expressions using
FullForm (possibly with Hold to prevent evaluation) to determine their
true structure. This resolved a host of puzzles:

In[1]:= x y //FullForm
Out[1]//FullForm= Times[x,y]

In[2]:= xy //FullForm
Out[2]//FullForm= xy

In[3]:= x*y //FullForm
Out[3]//FullForm= Times[x,y]

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

[Peter Pein]

Am 12.03.2013 05:34, schrieb Rahul Chakraborty:

Hi rc,

this occurs because you used a variable named "xy", not the product
"x*y" (or a space in place of the asterisk ("x y")).

Peter

[Richard Fateman]

try using x^2+2*x*y

xy is not the same as x*y

[Dr. Wolfgang Hintze]

On 12 Mrz., 05:34, Rahul Chakraborty <rahul.6s...@gmail.com> wrote:
> Dear all,
>
> Case1: In the following code
>
> Clear[f,x,y]
> g=Function[{x,y},x^2+2xy][b,a]
>
> The output is found to be b^2+2 xy
>
> Case2: But for the code
>
> Clear[f,x,y]
> g=Function[{x,y},x^2+2y][b,a]
>
> The output is 2 a+b^2
>

> Hence my query is why in case 1 x*y is not replaced by b and a whereas=

in case 2 it got replaced ?
>
> Regards,
> rc

It's a simple typo:
You must separate x from y in xy by * or space.
Regards,
Wolfgang

[svke...@aol.com]

In case one x*y didn't get replaced because it wasn't there; instead the variable xy was. Put a space between the x and the y:

In[3]:= Clear[f, x, y]

g = Function[{x, y}, x^2 + 2 x y][b, a]

Out[4]= 2 a b+b^2

[Frank K]

You need a space between the x and the y. What you have looks like a symbol xy, not x*y.

[Alexei Boulbitch]

Dear all,

Case1: In the following code

Clear[f,x,y]
g=Function[{x,y},x^2+2xy][b,a]

The output is found to be b^2+2 xy

Case2: But for the code

Clear[f,x,y]
g=Function[{x,y},x^2+2y][b,a]

The output is 2 a+b^2

Hence my query is why in case 1 x*y is not replaced by b and a whereas in case 2 it got replaced ?

Regards,
rc

Hi, Rahul,

Mathematica understands xy as a single new symbol, and, therefore, it does not interpret it as a product. If you want it to be multiplication you should make a space between x and y.
Then it works. Compare: this is your function

Clear[f, x, y]
g = Function[{x, y}, x^2 + 2 xy][b, a]

b^2 + 2 xy

and this is the same, but with the space between x and y:

Clear[f, x, y]
g = Function[{x, y}, x^2 + 2 x y][b, a]

2 a b + b^2

However, I prefer to put the sign "*" between x and y. Since it becomes quite clear from the first glance, what is x*y. Like this:

Clear[f, x, y]
g = Function[{x, y}, x^2 + 2 x*y][b, a]

2 a b + b^2

Have fun, Alexei



Alexei BOULBITCH, Dr., habil.
IEE S.A.
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