How to fill up missing values in a matrix?

Hi if i have matrix (6 by 4) like the following:

11 1 1
12 4 3
13 3 3  
14 2 3
15 4 7
16 3 4

I need to make up the missing values of different columns by the previous value of the respective columns. missing values in the first value of a column will be replaced by the next immediate available value. Can any one please help me by showing the MATLAB code to do this? This will be much appreciated.

Sayeed

[Walter Roberson]

How do you know if a value is missing?

Answer 1

[Image Analyst]

Not sure which elements are missing since HTML for some reason compresses all multiple spaces into one space. How about interp()?