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Mathematica 5.2

  1. Apr 28, 2007 #1


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    Hey. I just started using mathematica 5.2, and having a little trouble. When using the Solve[] function, the solutions are given as lists:

    {{t -> a}, {t -> 4}}

    In my next step of calculations, i want to use my second solution. How can i refer to it, instead of having to type it out. Now i know that if the solution was infact 4 that it would be easier to type it, but the solutions are not always as simple.

    Last edited: Apr 28, 2007
  2. jcsd
  3. Apr 28, 2007 #2
    the short answer is:

    t /. {{t -> a}, {t -> 4}}

    The solution is returned in the form of a replacement rule,the " /. " should be read as "replace". (look up the functions Rule and Replace in help). Replacement rules are extremely important.

    When you encounter a puzzling expression, try the function FullForm to see what its made of so you can look up the individual parts in the extensive Built-In help.
  4. Apr 29, 2007 #3


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    Ahh yes that makes sense. Thanks for that :smile:

    I now have a new question. I want to solve an equation, but the solution must lie within a restricted range of values. I assumed the following would work:

    Solve[ y[t]==0, t, {t,a,b}]

    However, it doesnt. I had a look at the built in help browser, and wasnt able to come up with anything. What should i do?
    Last edited: Apr 29, 2007
  5. Apr 29, 2007 #4
    A simple method in two lines:

    rangeQ[x_] = a ≤ x ≤ b;

    Select[ t/.Solve[y[t] == 0, t] , rangeQ ]

    Using a pure function in one line:

    Select[ t/.Solve[y[t] == 0, t] , a ≤ # ≤ b &]

    This preserves them as rules, rather then values:

    Select[ Solve[y[t] == 0, t] , a ≤ Last[#] ≤ b &]

    Hope that helps.
  6. Apr 30, 2007 #5
    Try "Part" command as Part[Solve[(t - a)*(t - 4) == 0, t], 2, 1, 2]
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