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how to enter a formula into excel ?

  • 02-11-2010 9:06pm
    #1
    rowa
    Closed Accounts Posts: 2,296 ✭✭✭


    i want to enter a formula into excel 2007, its from runge kutta and is v(t)=gm/c (1-e-(c/m)t)

    anyone any idea how to do this ? its the analytical formula .

    thanks.


Comments

  • #2
    bnt
    Registered Users, Registered Users 2 Posts: 13,076 ✭✭✭✭bnt


    Well, Excel works only with numbers, so you'd set up a range for the independent variable t, typically in a column. Assuming all the other variables on the RHS are constants, you assign a value to each in its own cell.

    Then, for each value of t, you calculate v(t) (usually in the next column to t), referring to all the other values. You hit F4 when selecting the constants, so that the references are locked (e.g. $A$4). Then copy the result you got for v(t) down, so that you have v(t) for every value of t.

    But I suspect there's more to your question than that. By "runge kutta" do you mean the Runge-Kutta method? That's not simply a formula, it's a method. If you can't do it on paper, you're not going to be able to do it in Excel, since Excel just does what you tell it to, and won't understand the problem for you!

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  • #3
    rowa
    Closed Accounts Posts: 2,296 ✭✭✭rowa


    yes i can do it on paper , but i am very inexperienced with excel , thanks for the answer.


  • #4
    Thoie
    Registered Users, Registered Users 2 Posts: 6,344 ✭✭✭Thoie


    If bnt is right, and everything is a constant except t, then let's put t into cell A1 and the answer v(t) into cell A2.
    I can't be bothered looking up the constants (as it's very late and I'm lazy), so I'll say
    g=5
    m=10
    c=15
    e=20 - just to give you the idea.

    So in cell A2 you type

    =((5*10)/15)*((1-20)-((15/10)*A1))

    The other assumption I'm making is that
    v(t)=gm/c (1-e-(c/m)t) ==> (gm/c) x (1-e- ((c/m) x t))
    Adjust the brackets if that's not right.


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