How can I do this matrix ?

I have this Matrix

A=[1;6;9;4;2;8]

I would like to generate a matrix as follow

the first row has only 1 and the rest zeros.

the seconds row has 1 and 6 and the rest zeros

the third has 1 , 6 and 9 and the rest zeros and so one

B=
  1 0 0 0 0 0
  1 6 0 0 0 0
  1 6 9 0 0 0   
  1 6 9 4 0 0  
  1 6 9 4 2 0
  1 6 9 4 2 8

How can I do it ?

Answer 1

[Stephen23]

>> A = [1;6;9;4;2;8];
>> M = tril(repmat(A.',6,1))
M =  
   1   0   0   0   0   0
   1   6   0   0   0   0
   1   6   9   0   0   0
   1   6   9   4   0   0
   1   6   9   4   2   0
   1   6   9   4   2   8

[zeezo]

Thank you very much

[zeezo]

Now If i want to just select a small matrix from this matrix

   1   0   0   0   0   0
   1   6   0   0   0   0
   1   6   9   0   0   0
   1   6   9   4   0   0
   1   6   9   4   2   0
   1   6   9   4   2   8

just 3*3

   C=
   1   0   0   
   1   6   0  
   1   6   9

How Can I do it ?

[Stephen23]

M(1:3,1:3)

[zeezo]

Thanks a lot