How can I multiply a vector by a scaling value with a loop?

Hi I have a vector A (1x200) and I want to multiply it for a scaling factor of 0.2 for 10 times. I would like to obtain a matrix B(10x200) where each row is the scaled vector?

thanks

Answer 1

[Jan]

A = rand(1, 100);
S = 0.2 .^ (1:10).';
B = S .* A;

A smaler example:

A = rand(1, 4)

A = 1×4

0.3654 0.1529 0.0723 0.4163

S = 0.2 .^ (1:3).'

S = 3×1

0.2000 0.0400 0.0080

B = S .* A

B = 3×4

0.0731 0.0306 0.0145 0.0833 0.0146 0.0061 0.0029 0.0167 0.0029 0.0012 0.0006 0.0033

[Paola]

thanks Jan,

it doesn't work because I have multiply the new vector for 0.2 up to ten times to obtain a matrix with 10 rows. Basically I have to scale my vector per 0.2 for 10 times.

[Voss]

I believe that is what @Jan's answer does (using 5 elements here instead of 100 for ease of display):

A = rand(1, 5);
S = 0.2 .^ (1:10).';
B = S .* A;

format long
disp(A);

   0.928773205480852   0.372047849369982   0.597515763533504   0.191352119560953   0.541467764860118

disp(B);

   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.037150928219234   0.014881913974799   0.023900630541340   0.007654084782438   0.021658710594405
   0.007430185643847   0.002976382794960   0.004780126108268   0.001530816956488   0.004331742118881
   0.001486037128769   0.000595276558992   0.000956025221654   0.000306163391298   0.000866348423776
   0.000297207425754   0.000119055311798   0.000191205044331   0.000061232678260   0.000173269684755
   0.000059441485151   0.000023811062360   0.000038241008866   0.000012246535652   0.000034653936951
   0.000011888297030   0.000004762212472   0.000007648201773   0.000002449307130   0.000006930787390
   0.000002377659406   0.000000952442494   0.000001529640355   0.000000489861426   0.000001386157478
   0.000000475531881   0.000000190488499   0.000000305928071   0.000000097972285   0.000000277231496
   0.000000095106376   0.000000038097700   0.000000061185614   0.000000019594457   0.000000055446299

The first row of B is 0.2*A, and each successive row is 0.2 times the previous row.

If you want 10 copies of 0.2*A instead, you can say:

B = repmat(0.2*A,10,1);
disp(B);

   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024

[Jan]

@Paola : I've inserted a small example. If this does not do, what you need, explain the difference. Give e.g. a small example of what you need instead.

What exactly does this mean: "multiply it for a scaling factor of 0.2 for 10 times"?