Calculating the sum of the absolute differences of a matrix

Hi all,

I have matrix X

x=[0 0 1 2 4 2 5 1 0 0 3 7 9 6 9 0 0 0 0 3 7 0 0 0 2];

how I could calculate the sum of the differences of the absolute values of the first 3 values from the last zero in the string of zeros?

So my output should be:

out = [ (1-0 + 2-1 + 4-2) , (3-0 + 7-3 + 9-7), .....], therefore

out = [ 4, 9....]

Please note that in my actual matrix X, there are positive and negative values so that's why I need the code to take the absolute value.

Thanks guys! Chris

Answer 1

[per isakson]

Here is a script that builds on my answer to your last question

x   = [0 0 1 2 4 2 5 1 0 0 3 7 9 6 9 0 0 0 0 3 7 0 0 0 2];
% add trailing [0,0] to avoid the risk of referencing outside x.
x(end+1:end+2) = [0,0];     
dx  = [ 0, diff( x ) ];
is0 = [ false, ( x == 0 ) ];
is0(end) = [];
ix_start = find( is0 & not(dx==0) );
an1 = nan( size( ix_start ) );
an2 = cell( size( ix_start ) );

for jj = 1 : length( ix_start )
    an1(jj) = sum( x( ix_start(jj)   : ix_start(jj)+2 ) );
    an2{jj} = abs( x( ix_start(jj)   : ix_start(jj)+2 ) ) ...
            - abs( x( ix_start(jj)-1 : ix_start(jj)+1 ) );
end

inspect new result

>> an2{:}
ans =
     1     1     2
ans =
     3     4     2
ans =
     3     4    -7
ans =
     2    -2     0
>>