## How to re-size a vector with new element obtained from old ones?

### Ayob (view profile)

on 20 Apr 2013

I need to create a new vector which is re-sized type of a vector and it's elements are obtained from previews vector.

for example:

```V1=[1 3 9 11]
```
```V2=[3*(1)-2,3*(1)-1,3*(1)-0,3*(3)-2,3*(3)-1,3*(3)-0,3*(9)-2,3*(9)-1,3*(9)-0,3*(11)-2,3*(11)-1,3*(11)-0]
```

As you can see vector V2 is made of vector V1. Each element of vector V1 in a special mode.

How can I write a code that build up V2 from V1 and be fast at the same time because I should do it several times and time is important to me.

Image Analyst

### Image Analyst (view profile)

on 20 Apr 2013

What's wrong with the way you're doing it? Just replace 1 by V(1), 3 by V(2), 9 by V(3), and 11 by V(4). Should be faster than a rocket powered, greased cheetah on steroids.

Ayob

### Ayob (view profile)

on 2 May 2013

It's ugly and bring about much difficulty to check it when you have a large program like mine.

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### per isakson (view profile)

Answer by per isakson

### per isakson (view profile)

on 20 Apr 2013

This is my best guess:

```    %%
V1=[ 1, 3, 9, 11 ];
%%
V2  = [ 3*V1(1)-2, 3*V1(1)-1, 3*V1(1)-0 ...
,   3*V1(2)-2, 3*V1(2)-1, 3*V1(2)-0 ...
,   3*V1(3)-2, 3*V1(3)-1, 3*V1(3)-0 ...
,   3*V1(4)-2, 3*V1(4)-1, 3*V1(4)-0 ];```
```>> V2
V2 =
1     2     3     7     8     9    25    26    27    31    32    33
```

I submit this to learn if I'm correct so far. Can V1 take any length?

Zhang lu

### Zhang lu (view profile)

on 2 May 2013

```V1=[1 3 9 11];
a=[-2,-1,0];
V2=(repmat(3*V1',1,length(a))+repmat(a,length(V1),1))';
V2=V2(:)'
```

### Jan Simon (view profile)

Answer by Jan Simon

### Jan Simon (view profile)

on 2 May 2013
Edited by Jan Simon

### Jan Simon (view profile)

on 2 May 2013

```V1 = [1, 3, 9, 11];
a  = [2, 1, 0];
V2 = reshape(bsxfun(@minus, V1, a(:)), 1, []);
```

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