How to load an indexed vector into a symsum?

I would like to load specific values into the symsum of each step, however it seems like i can't use the index of the sum as an index in my vector.

alpha=[1:100]; %example

syms D t 
S1=symsum(alpha(n)*exp(-D*alpha(n)*t),n,1,100);

Error using sym/subsindex (line 836)
Invalid indexing or function
definition. Indexing must follow
MATLAB indexing. Function arguments
must be symbolic variables, and
function body must be sym
expression.

I understand that Matlab see n as a symbol and the cant use it in the alpha(n) vector. How can i circumvent this bump?

Answer 1

[Birdman]

Try this:

alpha=1:100;
syms D t n
S1=symsum(alpha.*exp(-D.*alpha.*t),n,1,100);

[Andreas Pedersen]

Ahhh ofc course - use the matrix multiplikation, as long as length of alpha is the same as the length of the sum!

[Birdman]

Yes, little tricks about symbolic toolbox :)

If the answer helped, can you accept it?