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Mathematica problem - please help!

  1. Apr 21, 2005 #1
    I'm very new to mathematica and have been trying to use it for solving differential eqns. I've done a simple equation and managed to do a plot of it which looks correct. All day i've been trying to get findroot to work so i can find the exact point at which it crosses the x-axis but keep having problems. Attached is a screenshot of what i've done. If anyone can help i'd appreciate it.
     

    Attached Files:

  2. jcsd
  3. Apr 21, 2005 #2
    Fortunately for you and I, the problem is as simple as could be: In mathematica, rules only assign values during the instance you use them. What I mean is, everytime you want mathematica to recognize Phi(t) as the solution to your differential equation, you have to include

    Phi(t)/.Simpletreb

    NDSolve gives a rule as output. You named the rule simpletreb (sp?). What I mean is that your must change your code to this:

    FindRoot[Phi(t)/.simpletreb,{t,.2}]
     
  4. Apr 22, 2005 #3
    Thanks a lot! Very much appreciated. You can tell i'm new to this. I've been trying everything for days now. Problem solved! :smile:
     
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