MATLAB: I want to create a matrix where each column is obtained by subtracting 1 from the previous column.

matrix manipulation

For example: A=[4 3 2 1 0; 3 2 1 0 -1; 1 0 -1 -2 -3]

Best Answer

Use a loop, repmat or bsxfun. e.g:

startcolumn = [4; 3; 1];
numcolumns = 5;
A = bsxfun(@minus, startcolumn, 0:numcolumns-1)

Related Solutions

MATLAB: Matrix indexing using a vector

You can use sub2ind for this:

>> A = zeros(4,3);
>> col = [2;1;2;3];
>> row = 1:numel(col);
>> A(sub2ind(size(A),row(:),col(:))) = 1
A =
   0   1   0
   1   0   0
   0   1   0
   0   0   1

MATLAB: Subtract column from previous column in for loop

Presuming I infer your meaning precisely...

>> x=randi(200,4,3)                 % sample dummy data 
x =
 127   182    88
 198   115   121
 127    68   145
 121   192   136
>> y=diff(x,[],2)            % difference by column (note dummy placeholder for nth deriv)
y  =
  55   -94
 -83     6
 -59    77
  71   -56
>> y=bsxfun(@mrdivide,y,range(y))      % compute difference/range(difference)
y =
  0.3571   -0.5497
 -0.5390    0.0351
 -0.3831    0.4503
  0.4610   -0.3275
>>

NB: In recent releases of Matlab, the above expansion using bsxfun will be done automagically simply by writing

y=y./range(y);

I'm limited to R2014b here which predates that syntax introduction...

Best Answer

Related Solutions

MATLAB: Matrix indexing using a vector

MATLAB: Subtract column from previous column in for loop

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