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Re: Simple Problem (I suppose...)

• To: mathgroup at smc.vnet.net
• Subject: [mg22127] Re: [mg22102] Simple Problem (I suppose...)
• From: "David Park" <djmp at earthlink.net>
• Date: Wed, 16 Feb 2000 02:34:43 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Hi Andreas,

I think you have a lot of newbie errors in entering the characters.

1) Remove["Global`*"]
You must use the "backquote" in the upper left hand part of the keyboard. You used
the regular quote.  Use ` instead of '.

2) f[x_] := x^5 + x^4 + x^2
The thing following the x is the underscore character. You used a subscript. You
don't want a subscript here. The plot failed because it had no definition for f[x]
and so couldn't get a number value.

3) f2[x_] = D[f[x], x]
The same problem here. You need the underscore after the x, and your original f
definition was still bad.

4) f2[x] = D[f[x], x]
This didn't work because the original f definition was still bad. Also you will
generally not wish to make definitions that way because it will only work with x and
not other variables.

I would recommend working through as much of Part I of the Mathematica Book as you
can, typing in each of the statements until you get the hang of entering statements.
The two dimensional statements take a little practice.

For sending to MathGroup if often helps to convert the cells to InputForm
(Ctrl-Shift-I).

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


>Hi!
>
>I just got Mathematica 4 and when I try such easy calculations as below
>and then I can't plot the result.... WHY?? I really have no clue.
>
>Thanks,
>
>Andreas.
>
>Here my text is clipped:
>"
>In[1]:=
>Remove["Global'*"]
>
>Remove::"rmnsm": "There are no symbols matching \"\!\(\"Global'*\"\)\"."
>
>In[2]:=
>\!\(f[\(x\_-\)] := \ x\^5 + x\^4 + x\^2\)
>
>In[3]:=
>Plot[f[x], {x, -10, 10}];
>
>Plot::"plnr": "\!\(f[x]\) is not a machine-size real number at \!\(x\) =
>\
>\!\(-9.999999166666667`\)."
>
>Plot::"plnr": "\!\(f[x]\) is not a machine-size real number at \!\(x\) =
>\
>\!\(-9.188660168541684`\)."
>
>In[4]:=
>\!\(f2[\(x\_-\)]\  = \ \[PartialD]\_x f[x]\)
>
>Out[4]=
>\!\(\*
>  RowBox[{
>    SuperscriptBox["f", "\[Prime]",
>      MultilineFunction->None], "[", "x", "]"}]\)
>
>In[5]:=
>?f2
>
>In[6]:=
>\!\(f2[x]\  = \ \[PartialD]\_x f[x]\)
>
>Out[6]=
>\!\(\*
>  RowBox[{
>    SuperscriptBox["f", "\[Prime]",
>      MultilineFunction->None], "[", "x", "]"}]\)
>"
>
>