Re: How do you input a solution from FindRoot into another equation?
- To: mathgroup at christensen.cybernetics.net
- Subject: [mg771] Re: How do you input a solution from FindRoot into another equation?
- From: j-guyer at nwu.edu (Jon Guyer)
- Date: Tue, 18 Apr 1995 01:05:15 -0400
- Organization: Northwestern University, Evanston, IL
In article <3mieag$cl0 at news0.cybernetics.net>,
wagner at bullwinkle.cs.Colorado.EDU (Dave Wagner) wrote:
>You can extract the right-hand side of a rule by subscripting part 2:
[bizarre (no offense, Dave) machinations with sublists omitted]
In[1]:= FindRoot[BesselJ[0,x], {x,2.}]
Out[1]= {x -> 2.40483}
In[2]:= x/.%
Out[2]= 2.40483
In[3]:= Solve[x^2==2, x]
Out[3]= {{x -> -Sqrt[2]}, {x -> Sqrt[2]}}
In[4]:= x/.%
Out[4]= {-Sqrt[2], Sqrt[2]}
In[5]:= Solve[{x^2-2 == y, x+y==0}]
Out[5]= {{y -> -1, x -> 1}, {y -> 2, x -> -2}}
In[6]:= x/.%
Out[6]= {1, -2}
In[7]:= y/.%%
Out[7]= {-1, 2}
In[8]:= {x,y}/.%5
Out[8]= {{1, -1}, {-2, 2}}
Use the "/." (ReplaceAll) operator. It saves _much_ trouble in figuring
out which subscript to use. It's what you're "supposed" to use in this
case. The definition for this operator is
"expr /. x -> value replace 'x' by 'value' in the expression 'expr'"
--
Jonathan E. Guyer j-guyer at nwu.edu