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Problem of summation-mathematica

  1. Jan 13, 2012 #1
    MATHEMATICA:differentiate the summation

    I need help.im having problem to differentiate my equation respect to the m_i;How can i differentiate the equation.
    Second question is;When i set Y=2;how can i put the parameter like m_1;m_2;S_1;S_2;
    what i just do is input it manually by changing m_1=m1;m_2=m2;
    its very difficult if Y become larger number
    Code (Text):

    Sum[(Subscript[\[Sigma], i] - Subscript[c, i])*(Subscript[q, i]/
              Subscript[T, i]), {i, 1, Y}] -
       Sum[((1 - \[Beta])/(2 - \[Beta]))*(Subscript[d, i]*
          Subscript[q, i]) +
           (1/2)*((Subscript[m, i] - 1)*Subscript[w, i]*Subscript[q, i]) +
           (Subscript[A, i]/Subscript[m, i] + Subscript[S, i])/
             Subscript[T, i], {i, 1, Y}]
     
    Thanx for da help
     

    Attached Files:

    Last edited: Jan 13, 2012
  2. jcsd
  3. Jan 13, 2012 #2
    Y=2;
    s=Sum[...];
    d=D[s,Subscript[m,1]];
    d/.Subscript[m,1]->4
     
  4. Jan 13, 2012 #3
    Thanx a alot for da help.but what is da function of
    Code (Text):
     d /. Subscript[m, 1] -> 4  
    and do you know how can input the subscript like m_1 and m_2 if they have value ?
     
  5. Jan 13, 2012 #4
    expression/.variable->value
    is an alternate way of writing the ReplaceAll function.
    That function replaces all variable with value in expression.
    Here is the documentation for ReplaceAll.
    http://reference.wolfram.com/mathematica/ref/ReplaceAll.html
    If you look at the value of the variable d in my code and compare that
    with the value after the ReplaceAll you can see what it has done.

    I am not certain I understand what you mean "if they have value."
    If they have value then they are not a variable in your expression
    and there is no variable to replace with a value.
     
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