Re: Reducing for loop

[Markus Bergholz]

On Wed, Mar 25, 2015 at 9:09 PM, Dr.-Ing. Dieter Jurzitza <address@hidden> wrote:

Dear listmembers,
I am using a for loop as follows. I have an array, say A, containing numelem
elements.

Now I want to fill array B with elements as follows:

B(1)=A(1)

for i=2:numelem
   B(i)=B(i-1)+A(i);
endfor

looks like cumsum(A)

octave:13> A = 1:10;
octave:14> B = zeros(1,10);
octave:15> B(1) = A(1);
octave:16> for n = 2:numel(B), B(n) = B(n-1) + A(n); end
octave:17> all(B == cumsum(A))
ans =                    1

 

In order to get this vectorized I tried to write something like

B(1)=A(1) # IMHO no way around ...

# apparently does not work ...
for i=2:n
   B=A(i)+B(i-1);
endfor

What am I doing wrong here? Apparently using the indexed left - side array on
the right side is causing trouble ... Many thanks for any explanation in
advance,
take care




Dieter Jurzitza


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