Replace constant in summation function using replace or If or /

Question

Hi i how do i replace constant for k in this summation.

For following:

Here is the code

ue[x_, t_, k_, n_] := 
           (1/2)*Sum[Subscript[k, j]*(Subscript[x, j - 1][t] - Subscript[x, j][t])^2,{j, 1, n + 1}];

Roman · Accepted Answer · 2019-03-13 01:00:10Z

2

Subscript[k, j_?EvenQ] = a;
Subscript[k, j_?OddQ] = b;

For extra conditions at $j=0$ and $j=n+1$ you can use a two-index form $k_{n,j}$:

Subscript[k, n_, 0] = 0;
Subscript[k, n_, j_] /; j == n + 1 = 0;
Subscript[k, n_, j_?EvenQ] = a;
Subscript[k, n_, j_?OddQ] = b;

Check:

With[{n = 10}, Table[Subscript[k, n, j], {j, 0, n + 1}]]

{0, b, a, b, a, b, a, b, a, b, a, 0}

answered Mar 12, 2019 at 17:13

Roman

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$\begingroup$ sir how do i impose extra condition beside that above that k=0 at j=0 and j=n+1; k[0] = 0; k[n + 1] = 0; $\endgroup$
– Alrubaie
Commented Mar 12, 2019 at 18:14
$\begingroup$ ok i got it sir. thanks $\endgroup$
– Alrubaie
Commented Mar 12, 2019 at 18:20
$\begingroup$ Subscript[k, j_?EvenQ] = a; Subscript[k, j_?OddQ] = b; "to impose extra condition on beside that above that k=0 at j=0 and j=n+1; use " for n=4; Subscript[k, 0] = 0; Subscript[k, 4] = 0; $\endgroup$
– Alrubaie
Commented Mar 12, 2019 at 19:10

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