Re: Solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg8470] Re: [mg8458] Solve*From*: "w.meeussen" <meeussen.vdmcc at vandemoortele.be>*Date*: Tue, 2 Sep 1997 16:15:06 -0400*Sender*: owner-wri-mathgroup at wolfram.com

hi Saeed, you hit on a Mma 3.0 bug. two things: ** first ** remark that i only occurs as sin(i), so define y=sin(i). Then: In[28]:= y1= (1+q)*(0.38+0.2*Log[q])/2.844 Out[28]= 0.351617 (1 + q) (0.38 + 0.2 Log[q]) In[48]:= {c,d}=y/.Solve[q== ((2844/1000) y/Sqrt[1-y^2])-1,y] Out[48]= 2 62500 + 125000 q + 62500 q {-Sqrt[----------------------------], 2 568021 + 125000 q + 62500 q 2 62500 + 125000 q + 62500 q Sqrt[----------------------------]} 2 568021 + 125000 q + 62500 q this solves your problem; plot it with: In[38]:= Plot[{y1,c,d},{q,0,7}] it shows a intersection around y=0.84 and q=2.94. *** second *** you hit on an error by accident: In[47]:= {a,b}=y/.Solve[q== (2.844 y/Sqrt[1-y^2])-1,y] Out[47]= {-1. Sqrt[62500.00000000000000000000000000 + 125000.00000000000000000000000000 q + 2 62500.00000000000000000000000000 q ], Sqrt[62500.00000000000000000000000000 + 125000.00000000000000000000000000 q + 2 62500.00000000000000000000000000 q ]} somehow produces garbage ! Compare "2." (floating point) and "2" as integer : with rhe floating point input, the denominator "evaporates" !! REEKS OF BUG !! In[52]:= {a,b}=y/.Solve[q== (2. y/Sqrt[1-y^2])-1,y] Out[52]= {-1. Sqrt[1.0000000000000000000000000000000 + 2 2.0000000000000000000000000000000 q + q ], Sqrt[1.0000000000000000000000000000000 + 2 2.0000000000000000000000000000000 q + q ]} In[53]:= {a,b}=y/.Solve[q== (2 y/Sqrt[1-y^2])-1,y] Out[53]= 2 2 1 + 2 q + q 1 + 2 q + q {-Sqrt[------------], Sqrt[------------]} 2 2 5 + 2 q + q 5 + 2 q + q At 00:43 30-08-97 -0400, Saeed Esmaily Rashid wrote: >Hello! > >I'm a physics student, using Mma 3.0.0. My problem is to plot two functions >simultaneously finding their intersection. The functions are > >sin(i) < (1+q)*(0.38+0.2*log(q))/2.844 > >and > >q > (2.844*sin(i)/sqrt(1-sin(i)^2))-1. > >The graph must be such that one axis is sin(i) the other is q. I tried using >the Plot function in Mma but i didn't get the desired solution. Any attampt >to solve these equations using Solve[], fails leaving me with no answer. >I'll be grateful of any help. > >Thanks > > > > > Dr. Wouter L. J. MEEUSSEN eu000949 at pophost.eunet.be w.meeussen.vdmcc at vandemoortele.be