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Re: [mg5307] Rule to Function, Frontend funnies
Posted:
Nov 26, 1996 3:38 AM


> how can I convert a rule to a function? > if I get a result from > > rulesoln = DSolve[{y'[x]==y[x]/(c+1/x),y[0]==1},y[x],x] > > in the form : > > 2 > x/c  Log[1 + c x]/c > {{y[x] > E }} > > how do I get the definition : > > y[x_]:= E^(x/c  Log[1 + c x]/c^2) > > Anybody out there to whom this happens too? > After some {soul,FullForm}searching, I came up with this ruleeatingrule : > > Flatten[rulesoln]/.y[x]>y[x_]/.Rule>SetDelayed > > {Null} > > you don't get to see much except "{Null}", but it results in: > > ?y > > Global`y > y[x_] := E^(x/c  Log[1 + c*x]/c^2) > > (*************************************************************************) > > Is there a fast & easy CutandPaste way to do it, not leaving the FrontEnd? > Is this the same on a Macmachine? > Is this the same in Mma 3.0 for Windows? > What do You want? The SetDelayed is evaluated and the result of it is Null. The best is to make a definition
thisSolutionY[x_]:=y[x] /. Flatten[rulesoln]
How ever if You don't want to evaluate Your delayed rule You can do the following In[27]:= Clear[y]
In[28]:= rulesoln=DSolve[{y'[x]==y[x]/(c+1/x),y[0]==1},y[x],x] //InputForm
Out[28]= {{y[x] > E^(x/c)/(1 + c*x)^c^(2)}}
In[29]:= sol=rulesoln[[1,1,1]] //InputForm Out[29]//InputForm= y[x] > E^(x/c)/(1 + c*x)^c^(2)
In[31]:= Hold[Evaluate[sol] ]/. {y[x] :> HoldPattern[y[x_]],Rule>SetDelayed} Out[31]= Hold[HoldPattern[y[x_]] := E^(x/c)/(1 + c*x)^c^(2)]
now You see the definition. A simple
In[32]:=ReleaseHold[%]
will evaluate this. With Mma 2.2 You must use Literal instead of HoldPattern. Somewehre in Your 2.2 Frontend is the command  Copy Output from above.
Hope that helps Jens



