[Haskell-cafe] cumulative sum

[Chad Scherrer]

Tamas,

try
scanl (+) 0
for the cumulative sum

>From there the zipWith idea you mentioned seems like the way to go.

-Chad

> Hi,
>
> I have two lists, p and lambda (both are finite).  I would like to
> calculate
>
> 1) the cumulative sum of lambda, ie if
>
> lambda = [lambda1,lambda2,lambda3,...]
>
> then
>
> csum lambda = [lambda1,lambda1+lambda2,lambda1+lambda2+lambda3,...]
>
> 2) the cumulative sum of p*lambda (multiplication elementwise)
>
> Once I know how to do the first, I know how to do the second I guess
> (doing the multiplication using zipWith to get the p*lambda list, but
> I would be interested in any other suggestions).  Currently I take and
> sum, but then I am calculating the same sums many times.
>
> Thanks,
>
> Tamas