How to create an array of the form [1,2,4,7,11,16] without the use of a loop?

Is is possible to create a Matlab array where the jump between two consecutive numbers is not constant but increases by 1 every time?

Answer 1

[Star Strider]

It is, using the cumsum function (and a bit of fudging to get the result you want):

x = 1:5;
xs = [1 1+cumsum(x)] 

xs =

       1     2     4     7    11    16

[Ralph]

Thanks a lot!

[Star Strider]

My pleasure!

A more efficient approach (that I was just going to post) is:

x = 0:5;
xs = 1+cumsum(x)

giving the same result.

[Image Analyst]

To make it a little more general, you can do this:

numElements = 5;
startingValue = 10;
x = 0:(numElements-1);
xs = startingValue + cumsum(x)

Or if cumsum() is a little hard to follow or understand, you can use a for loop:

% Define parameters
startingValue = 10;
numElements = 5;
% Now construct an array that has a first value of startingValue
% and has numElements total number of elements,
% where each element increases by 1, 2, 3, 4, ...
% from the element before it.
x = startingValue % Initialize first element.
for k = 2 : numElements
  x(k) = x(k-1) + (k-1);
end
% Show in command window.
x