How to remove a value from a vectort and revaluate it?

Hi

I'm trying to create a vector from a random number drawn from a normal distribution.

maxiter=1000;

M=zeros(maxiter,1);
M=(0.8+0.8*randn(maxiter,1));

Because negative numbers don't make any biological sense in this case, I would like have the negative values redrawn from the randn

    if M<0;
         Mtemp=M;
         while Mtemp<0;
               Mtemp=(0.8+0.8*randn);
               M=Mtemp;
         end
      else M=M;
      end;

This does not seem replace any of the negative values. Thanks for the help!

[David C]

I believe you need to look into logical indexing.

Matlab's specialty when dealing with matrices and vectors is logical indexing, so instead of your if/else block, you can simply use M(M<0)=[];

Answer 1

[Thomas]

Just editing your code..

maxiter=1000;

M=zeros(maxiter,1);
M=(0.8+0.8*randn(maxiter,1));

for ii=1:length(M)
if M(ii)<0;
         Mtemp=0.8+0.8*randn;

           while Mtemp<0;
                 Mtemp=(0.8+0.8*randn);
                 M(ii)=Mtemp;
           end
           M(ii)=Mtemp;
  end
  end

Answer 2

[Matt Fig]

There is no need to pre-allocate M, as M is not built in a FOR loop. You are just overwriting the pre-allocation in one call, so it is not necessary at all.

maxiter = 1000;
M = 0.8 + 0.8*randn(maxiter,1);
idx = M<0;

while any(idx)
   M(idx) = 0.8+0.8*randn(sum(idx),1);
   idx = M<0;
end