MATLAB insert value in between

in MATLAB i wish to 开发者_运维技巧insert a value half way between every element in the vector

for example

  v=[1,3,5,7,9]

i want to get

  v=[1,2,3,4,5,6,7,8,9]

is there a quick way to do this?

A very simple, general way to do this is with interpolation, specifically the function INTERP1:

>> v = [1 3 5 7 9]

v =

     1     3     5     7     9

>> v = interp1(v,1:0.5:numel(v))

v =

     1     2     3     4     5     6     7     8     9

a = [1 3 5 7 9];
b = [2 4 6 8];
c = zeros(9,1);
c(1:2:9) = a; c(2:2:8) = b;

Since you just want the average of each two values to be inserted, you could do the following:

v = [1 3 5 7 9];
W = zeros(1,2*numel(v)-1);
W(1:2:end) = v;
W(2:2:end-1) = (W(1:2:end-2) + W(3:2:end))/2

If you want something else, take a look at interp1, which will allow for more advanced interpolation.

if diff(v) is a constant, like your example [1 3 5 7 9], you can do it like this:

>> v=[1 3 5 7 9]  
v =
     1     3     5     7     9
>> w=linspace(v(1),v(length(v)),2*length(v)-1)
w =
     1     2     3     4     5     6     7     8     9

as the official help doc says:

y = linspace(x1,x2,n) generates n points. The spacing between the points is (x2-x1)/(n-1).

If diff(v) is not a constant ,like v=[1 3 6 8 10], you can first calculate the difference use

dv=diff(v)

then you can have w

w=ones(1,2*length(v)-1) %initialize
w(1:2:length(w))=v; % odd element
w(2:2:length(w)-1)=v(1:length(v)-1)+diff(v)*0.5  %even element