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Rayne
01/27/07 01:18am

Hi all,
I want to plot the cubic equation f(x) = x^3 - 16x^2 + 3x + 1 = 0. I had:

f=x^3-16 x^2+3 x+1 == 0
Plot[f,{x,-1,20}]

but I was unable to get the plot. The error message says

Plot::plnr: f is not a machine-size real number at x = -0.999999.
Plot::plnr: f is not a machine-size real number at x = -0.148093.
Plot::plnr: f is not a machine-size real number at x = 0.780985.
General::stop: Further output of Plot::plnr
will be suppressed during this calculation.

How do I get around this problem?

Also, I need to define a set of functions for vector calculus. Two of them are the gradient (equivalent to Del[f] in Mathematica) and the laplacian (equivalent to [CapitalDelta]).

I have:
gradient[f_]:={D[f,x],D[f,y],D[f,z]}
and
laplacian[f_]:=D[f,{x,2}]+D[f,{y,2}]+D[f,{z,2}]

As you can see, this only works if the function f has 3 variables. How do I make it more general, that is, for an arbitrary number of variables?

Also, how do I use the Del and CapitalDel functions in Mathematica? I tried Del[f] when f is 2x^3-3y^2+4z and only got \[Del](2 x^3 - 3 y^2 + 4 z) as output.

Thank you.

Regards,
Rayne


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Subject (listing for 'Plotting and defining functions')
Author Date Posted
Plotting and defining functions Rayne 01/27/07 01:18am
Re: Plotting and defining functions yehuda ben-s... 01/28/07 01:50am
Re: Plotting and defining functions Rayne 01/29/07 11:30am
Re: Plotting and defining functions yehuda ben-s... 01/30/07 02:34am
Re: Plotting and defining functions Rayne 01/31/07 05:57am
Re: Plotting and defining functions yehuda ben-s... 01/31/07 09:37am
Re: Plotting and defining functions Rayne 02/02/07 10:40pm
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