how to write a geometric series in command window

How do I write a vector that follows the geometric form: 1, 3, 6, 9...

[Stephen23]

"how to write a geometric series in command window... How do I write a vector that follows the geometric form: 1, 3, 6, 9..."

1,3,6,9 is not a geometric sequence.

A geometric sequence is defined as having a constant ratio between adjacent terms. The ratio of those terms is not constant.

Which of these sequences do you want?: https://oeis.org/search?q=1%2C+3%2C+6%2C+9

[Sami Ahmed]

the sequence must continue to 100(102), i understand that it is not a geometric sequence. my assignment is asking me to write the vector 1, 3, 6, 9

[Stephen23]

https://web.archive.org/web/20220908142417/https://www.mathworks.com/matlabcentral/answers/1799620-how-to-write-a-geometric-series-in-command-window

[Stephen23]

Have a look at specifying the step size:

3:3:10

ans = 1×3

3 6 9

The 1 at the start does not fit any obvious sequence.

[Sami Ahmed]

how can i add one to the beginning of a vector?

[Stephen23]

"how can i add one to the beginning of a vector?"

[1,yourVector]

Very basic MATLAB concepts, such as how to concatenate scalars and vectors together, are more efficiently learned by doing the introductory tutorials: https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

[Sami Ahmed]

sorry i understood that, now i mean to ask how can i make a vector n terms long. i want to make this vector 100 terms long...

[Torsten]

Just calculate:

100*3 = 300

so

b = 1./(3:3:300);
numel(b)

ans = 100

Note that 1 + 1/3 + 1/6 + 1/9 + ... is not a geometric series.

[Sami Ahmed]

ya ive got that thanks

[Torsten]

But note that you need 1 as first term followed by 99 terms of the form 1/(3*i).

1./(3:3:300) gives 100 terms of the form 1/(3*i).

Answer 1

[KSSV]

a = 1 ;
r = 2 ; 
n = 0:9 ;
gp = a*r.^n 

gp = 1×10

1 2 4 8 16 32 64 128 256 512

[Sami Ahmed]

1, 3, 6, 9....?

[Les Beckham]

Maybe you mean this?

a = 1 ;
r = 3 ; 
n = 0:9 ;
gp = a*r.^n 

gp = 1×10

1 3 9 27 81 243 729 2187 6561 19683

[Sami Ahmed]

i really dont know, my assignment is asking to create the vector: 1, 3, 6, 9

[Torsten]

This is not a geometric sequence.

For a geometric sequence, the quotient of two subsequent members of the sequence must be constant:

a(n+1)/a(n) = q = const. for every n.

In your case:

a2/a1 = 3

a3/a4 = 2

a5/a4 = 1.5

so the quotient is always different.

Answer 2

[David Hill]

sum(1./[1,3:3:297])

ans = 2.7258