Re: plot command
- To: mathgroup at smc.vnet.net
- Subject: [mg58126] Re: plot command
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Sun, 19 Jun 2005 03:43:29 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 6/18/05 at 6:07 AM, bosch at vt.edu (Bosch, Darrell) wrote:
>Dear Group: I am trying to solve an equation, take the derivative
>and plot the derivative as shown below. I get a message below the
>Plot request stating
>"Syntax::sntxi: "Incomplete expression; more input is needed." Any
>help would be greatly appreciated. Darrell Bosch
>sol = Log[v]=A9100*Log(s)
The line immediately above should have generated an error message. It asks Mathematica to set Log[v] to A9100*Log(s). Note, in Mathematica, the expression A9100*Log(s) isn't valid syntax. It would be parsed as the product of three variables A9100, Log and s. And since Log is already a reserved named, this is going to be a problem. Correct syntax would be:
sol = Log[v]==A91000*Log[s]
>sol2 = Solve[sol,v]
Making the change I indicated, sol2 should become
{{v -> s^A9100}}
a list of replacement rules, So,
>sol3 = D[sol2,s]
Needs to become
sol3 = D[v/.First@sol2,s]
which sets sol3 to
A9100*s^(A9100 - 1)
But, there is still one more thing to be done before this can be plotted. That is to assign a value to A9100. So, a plot could be generated as:
Plot[sol3 /. A9100 -> 1/2, {s, 0, 100}];
>Plot[Evaluate[sol3],{s,0,100}]
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