How do i use a pair of nested for loops to store a series of 9 related numbers in a 3x3 matrix?

the outer loop decides what row and the inner loop decides what column to store each number in the series, the code should prompt the user for the starting number and increment of the series

[James Tursa]

What have you tried so far? For-loops are quite easy to write. Have you looked in the doc for help?

[Sarah Mcmillan]

a=1
b=1
 X = zeros(3,3);
for a = 1:3
    for b= 1:3
        X(a,b) = (a+b)
    end

end

But my matrix looks like X =

     2     3     4
     3     4     5
     4     5     6
 instead of 1 being added to the next one

[David Goodmanson]

I Sarah,

not sure you mean by 'instead of 1 being added to the next one'. Evidently (a+b) is not quite what you are looking for.

Aside from that, one thing happening is that when you have the line 'for a = 1:3', then the previous statement a = 1 doesn't mean anything. You could have a = 54321 before the for loop, and the starting values for a at the beginning of the the loop are just 1,2,3. Same for b of course.

[Sarah Mcmillan]

I'm sorry for the confusion, I'm just frustrated. I am trying to do a pair of nested loops so that I can just denote a as the number I want to start with and b the number I want to continuously add. In the end I want my matrix to look like

[1,     2,     3;     
 4,     5,     6;    
 7,     8,     9]

for the case that a=1 and b=1, but I want to be able to change a and b to any numbers if I chose to do so.

Right now I have the matrix

[2,     3,     4;
 3,     4 ,    5;
 4,     5 ,    6]

as you can see the rows are adding by 1 but the columns are not continuing the counting, they add 1 to the number above it. I need help to figure out so that it continues the counting not whatever its doing now.

[David Goodmanson]

Does this have to be done with 'for' loops, or is any technique in Matlab all right to use?

Answer 1

[Dennis]

I hope i got the question right (some possible solutions with increasing number of loops):

   %no loop
    a=1;
    b=1;
    X=ones(1,9)*a;
    Y=ones(1,8)*b;
    Y=cumsum(Y);
    X(2:end)=X(2:end)+Y;
    X=reshape(X,[],3)';

%1 loop
a=1;
b=1;
X=ones(1,9)*a;
for i=1:numel(X)
    X(i)=X(i)+(i-1)*b;
end
X=reshape(X,[],3)';

%2 loops
a=1;
b=1;
X=ones(3,3)*a;
for i=1:3
    for k=1:3
        X(i,k)=a+(i*k-1)*b;
    end
end

Answer 2

[Stephen23]

"How do i use a pair of nested for loops to store a series of 9 related numbers in a 3x3 matrix?"

num = str2double(input('start number: ','s'));
nrows = 3;
ncols = 3;
mat = nan(nrows,ncols);
for kr = 1:nrows
    for kc = 1:ncols
        mat(kr,kc) = num;
        num = num+1;
    end
end

And when run:

start number: 1
>> mat
mat =
   1   2   3
   4   5   6
   7   8   9