matrix and vector indices out of range

Hi guys,

I have the following code:

K = 20*10^3;
X = zeros(1,K/2+1);

w = 10
wi = repmat(1:w,length(i),1);

wi =

       1     2     3     4     5     6     7     8     9    10
       1     2     3     4     5     6     7     8     9    10
       1     2     3     4     5     6     7     8     9    10
       1     2     3     4     5     6     7     8     9    10
       1     2     3     4     5     6     7     8     9    10

Xind = [751 1500 2250 2999 3749]; %this was actually calculated.

ind_plus_wi = bsxfun(@plus,wi,Xind');

ind_plus_wi =

Columns 1 through 10

752   753   754   755   756   757   758   759   760   761
1501  1502  1503  1504  1505  1506  1507  1508  1509  1510
2251  2252  2253  2254  2255  2256  2257  2258  2259  2260
3000  3001  3002  3003  3004  3005  3006  3007  3008  3009
3750  3751  3752  3753  3754  3755  3756  3757  3758  3759

i = 1:5;
i_M = repmat(i',1,w);

i_M =

       1     1     1     1     1     1     1     1     1     1
       2     2     2     2     2     2     2     2     2     2
       3     3     3     3     3     3     3     3     3     3
       4     4     4     4     4     4     4     4     4     4
       5     5     5     5     5     5     5     5     5     5

v = 1:5;

X(ind_plus_wi) = v(i_M);

Here, I defined X to have indices from 1:K/2+1 and I am using the values of ind_plus_wi to set values in X as such: X(ind_plus_wi) = v(i_M). But it is possible under certain circumstance for ind_plus_wi to have values that are outside the interval of X(1:K/2+1). I would like to skip over those. In the case where ind_plus_wi > K/2+1, I could just do X = X(1:K/2+1) and discard that data. However, if ind_plus_wi < 1, MATLAB will produce an error that I can't recover from. What can I do? Thanks!

Answer 1

[Leor Greenberger]

Thinking about it, I could probably do:

ind_plus_wi(ind_plus_wi < 1) = K/2+2

and

X(ind_plus_wi) = v(i_M);
X = X(1:K/2+1);

Answer 2

[Fangjun Jiang]

The problem is about the variable i.

Many people use i as a variable to do iteration in a for-loop, for example i=1:5.

Without knowing that i actually is a built-in constant. Do this:

clear all
length(i)
help i

In your code, you used length(i) first without assign value to i. So it is thinking that you are use i as the Imaginary unit. That is why it gives error.