How to add rows containing zeros to a matrix

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Dr Sohaib Khan on 27 Jul 2023
Commented: Dr Sohaib Khan on 28 Jul 2023
I have a "2x101" matrix, I want to add 4 rows to it, containing "zeros" to make it "6x101" matrix.
Please if anyone could guide me on syntax. Thankyou.

Cris LaPierre on 27 Jul 2023
A = rand(2,6)
A = 2×6
0.8131 0.2963 0.1224 0.8259 0.2399 0.5947 0.7303 0.1732 0.9839 0.2746 0.6453 0.7036
A(3:4,:)=0
A = 4×6
0.8131 0.2963 0.1224 0.8259 0.2399 0.5947 0.7303 0.1732 0.9839 0.2746 0.6453 0.7036 0 0 0 0 0 0 0 0 0 0 0 0
Dr Sohaib Khan on 28 Jul 2023
BiG FAT Thankyou :) Cris

Voss on 28 Jul 2023
Here's one way:
% a 2x101 matrix
a = rand(2,101)
a = 2×101
0.2749 0.6630 0.7375 0.2538 0.1755 0.5986 0.1725 0.4662 0.3609 0.7840 0.8763 0.3446 0.3603 0.8626 0.2283 0.1468 0.3254 0.3290 0.3960 0.4185 0.1099 0.0486 0.0626 0.7403 0.6850 0.4095 0.8703 0.1152 0.5754 0.7633 0.8014 0.8300 0.6248 0.5979 0.5868 0.4567 0.0246 0.0519 0.1590 0.1996 0.5126 0.0511 0.1397 0.9698 0.5512 0.3256 0.6557 0.6494 0.0743 0.7528 0.8313 0.6114 0.4597 0.6038 0.5030 0.9302 0.4747 0.8711 0.4699 0.2633
% append 4 rows of zeros
a = [a; zeros(4,size(a,2))]
a = 6×101
0.2749 0.6630 0.7375 0.2538 0.1755 0.5986 0.1725 0.4662 0.3609 0.7840 0.8763 0.3446 0.3603 0.8626 0.2283 0.1468 0.3254 0.3290 0.3960 0.4185 0.1099 0.0486 0.0626 0.7403 0.6850 0.4095 0.8703 0.1152 0.5754 0.7633 0.8014 0.8300 0.6248 0.5979 0.5868 0.4567 0.0246 0.0519 0.1590 0.1996 0.5126 0.0511 0.1397 0.9698 0.5512 0.3256 0.6557 0.6494 0.0743 0.7528 0.8313 0.6114 0.4597 0.6038 0.5030 0.9302 0.4747 0.8711 0.4699 0.2633 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Dr Sohaib Khan on 28 Jul 2023
BiG FAT Thankyou :) Voss

Les Beckham on 27 Jul 2023
Here is another way.
A = rand(2,6)
A = 2×6
0.5677 0.5655 0.2207 0.5221 0.5033 0.0094 0.1184 0.9091 0.7727 0.4403 0.6020 0.3454
A(4,6) = 0
A = 4×6
0.5677 0.5655 0.2207 0.5221 0.5033 0.0094 0.1184 0.9091 0.7727 0.4403 0.6020 0.3454 0 0 0 0 0 0 0 0 0 0 0 0
Dr Sohaib Khan on 28 Jul 2023
BiG FAT Thankyou :) Beckham

James Tursa on 27 Jul 2023
Edited: James Tursa on 27 Jul 2023
E.g., one way using the end syntax:
my_matrix = reshape(1:12,3,4)
my_matrix = 3×4
1 4 7 10 2 5 8 11 3 6 9 12
n = 4; % number of rows to append
my_matrix(end+n,1) = 0
my_matrix = 7×4
1 4 7 10 2 5 8 11 3 6 9 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Basically, setting any element in the 4th row beyond the current last row will cause MATLAB to append 4 rows of 0's to the matrix and set the particular element. I.e., MATLAB will dynamically increase the size of the matrix to accomodate the element you are trying to set, and all of the elements you don't set in the process are automatically set to 0's. In the above example, I set the (7,1) element to 0 explicitly, and MATLAB filled in all the other elements in the newly created four rows to 0's automatically.
Dr Sohaib Khan on 28 Jul 2023
Understood Great Help :) James Thankyou :)

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