Re: Newbie Plot-Fit Questions.

*To*: mathgroup at smc.vnet.net*Subject*: [mg31137] Re: [mg31116] Newbie Plot-Fit Questions.*From*: Tomas Garza <tgarza01 at prodigy.net.mx>*Date*: Fri, 12 Oct 2001 03:36:58 -0400 (EDT)*References*: <200110102314.TAA25712@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

It looks weird, doesn't it? The thing is, if you ask for the attributes of Plot you'll find that one of them is HoldAll, which specifies that all arguments to Plot are to be maintained in an unevaluated form. You must then force the argument (in this case, Fit[etc].) to be evaluated before it is sent to Plot. Try Plot[(Evaluate[ Fit[{{2942,3650782},{2955,2255796},{3204,730421},{4105,1740135},{7815, 6329111},{13097,7116844}},{1,x,x^2,x^3},x]]),{x,2942,13097}]] and the mystery will vanish. A useful discussion on the subject can be found in The Book, Section 1.9.1. Tomas Garza Mexico City ----- Original Message ----- From: "SkyBeaux" <realbeaux at yahoo.com> To: mathgroup at smc.vnet.net Subject: [mg31137] [mg31116] Newbie Plot-Fit Questions. > Please explain this to me: > > If I do the following: > > Fit[{{2942, 3650782}, {2955, 2255796}, {3204, 730421}, {4105, > 1740135}, {7815, > 6329111}, {13097, 7116844}}, {1, x, x^2, x^3}, x] > > Results are: > \!\(1.7044496230729986`*^7 - 8507.38287339198`\ x + > 1.3901134594316935`\ x\^2 - 0.00006096360495406324`\ x\^3\) > > Then I plot the results as follows: > > \!\(Plot[1.7044496230729986`*^7 - 8507.38287339198`\ x + > 1.3901134594316935`\ x\^2 - 0.00006096360495406324`\ x\^3, {x, > 2942, > 13097}]\) > > I get a nice "sin" looking plot. (This is what I want.) > > However if I try to combine the two statements into one. Like this: > > Plot[(Fit[{{2942, 3650782}, {2955, 2255796}, {3204, 730421}, {4105, > 1740135}, {7815, 6329111}, {13097, 7116844}}, {1, x, x^2, > x^3}, > x]), {x, 2942, 13097}] > > I get a linear chart. > > What is the difference? And how do I get my nice "sin" looking plot > back? > > As you can see, I an not really sure what is being plotted by the > first set of commands, but I think it is a log plot. > > Thanks for you help. > > --SB >

**References**:**Newbie Plot-Fit Questions.***From:*realbeaux@yahoo.com (SkyBeaux)