i want to code the following such that the negative values get saved in zerocoeff and then the negative values becomes zero . I have tried something but i m still getting an empty zerocoeff .

   for i5=1:vdim*rdim
    v(i5)=w(i5)+alpha(i5)*w(i5);
    if v(i5)<0
        zerocoeff = v(i5<0);  
    v(i5)=0;
else 
    v(i5)=v(i5);
end
end

Answer 1

[Jan]

What is the intention of "v(i5)=v(i5)"?

Do you need a loop?

v      = w + alpha .* w;
lt0    = (v < 0);
zerocoeff = v(lt0);
v(lt0) = 0;

Please use the debugger to examine what happens in your code. Set a breakpoint and step through the program line by line. Then you will see problems like "v(i5<0)", where the value of the index is checked, and not the value of the vector v.

Note that zerocoeff = v(i5<0) overwrites zerocoeff in each iteration.