how can i create this matrix

hello,

i'm new to this software and i couldn't find an explanation to this

I have a matrix that is defined like this:

A(ij) , 1<=j<=7 , 1<=i<=8

if i>j then 2j-1

if i<=j then 4j-2i

how can i write it in the software?

Thanks for your help

Answer 1

[Matt J]

A=nan(7,8);

[I,J]=ndgrid(1:7,1:8);

A(I>J)=2*J(I>J)-1;

...

[shlomo shnur]

it doesn't work for me .

i copied it to the command window and i got an error :

"Unable to perform assignment because the left and right sides have a different number of elements."

[Matt J]

Fixed.

Answer 2

[Stephen23]

>> [I,J] = ndgrid(1:7,1:8);
>> X = I>J;
>> M = (2+2*~X).*J.*X - 2.*~X.*I - X
M =
   -2   -2   -2   -2   -2   -2   -2   -2
    1   -4   -4   -4   -4   -4   -4   -4
    1    3   -6   -6   -6   -6   -6   -6
    1    3    5   -8   -8   -8   -8   -8
    1    3    5    7  -10  -10  -10  -10
    1    3    5    7    9  -12  -12  -12
    1    3    5    7    9   11  -14  -14

Answer 3

[shlomo shnur]

found a solution:

I=8;

J=7;

A=ones(I,J);

for I=1:8

for J=1:7

if I>J

A(I,J)=(2*J-1);

elseif I<=J

A(I,J)=(4*J-2*I);

end

end

end

2 6 10 14 18 22 26

1 4 8 12 16 20 24

1 3 6 10 14 18 22

1 3 5 8 12 16 20

1 3 5 7 10 14 18

1 3 5 7 9 12 16

1 3 5 7 9 11 14

1 3 5 7 9 11 13

thank you for the help !

[Stephen23]

Your matrix dimensions are swapped: matrices are defined by rows and columns, so your original specification "A(ij) , 1<=j<=7 , 1<=i<=8" requires a 7x8 matrix, not an 8x7 matrix like in your answer.

In any case, using loops is not a particularly neat use of MATLAB.