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Student Support Forum: 'Differentiation with Summation Symbol' topicStudent Support Forum > General > Archives > "Differentiation with Summation Symbol"

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Author Comment/Response
Paul J. Ferraro
10/10/99 7:15pm

I am trying to take the partial derivative of an expression that
sums an equation with time-subscripted elements from t=1 to
t=infinity. I want to take partials of the equation with respect to
different time-subscripted variables in the equation; e.g., D[l ,
ct], where l is the defined equation and c subscript t is one of the
variables. Mathematica, however, simply returns the entire
expression with a partial sign between the summation symbol
and the equation. It doesn't actually solve for the derivatives of
each of the elements of the equation (some of the elements of the
equation are generic functions, like u[ct, Lt], while others are
more explicit, like lambda*ct). If I get rid of the summation
sign, Mathematica does solve for the derivative (i.e., the
derivative of each element is taken and expressed on the screen).

Any suggestions? Thanks.

Paul Ferraro


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