Subscripted assignment dimension mismatch. What should i do?

So basically I downloaded the data provided by my professor and somehow when I worked on creating 2 coloumn for x, it said "Subscripted assignment dimension mismatch" and i got stuck... Here are my steps,

>> Y(:,1)=mgtndvi(:,1)

Y =

    0.0485
   -0.1794
    0.1378
    0.0124
    0.0723
    0.1893
    0.1344
    0.1159
    0.1765
    0.1340
    0.1504
    0.1257
   -0.0646

>> mgtndvi=dlmread('mgt-ndvi0082-2.txt')

mgtndvi =

    0.0485    4.2091
   -0.1794    5.2015
    0.1378    3.4137
    0.0124    4.3957
    0.0723    3.0455
    0.1893    2.3837
    0.1344    3.0349
    0.1159    3.0462
    0.1765    2.9660
    0.1340    3.5063
    0.1504    2.5861
    0.1257    3.7062
   -0.0646    4.5121

>> X(:,1)=ones(12,1)

X =

     1
     1
     1
     1
     1
     1
     1
     1
     1
     1
     1
     1

>> X(:,2)=mgtndvi(:,2) Subscripted assignment dimension mismatch.

and if I changed X into Y, it works

>> Y(:,2)=mgtndvi(:,2)

Y =

    0.0485    4.2091
   -0.1794    5.2015
    0.1378    3.4137
    0.0124    4.3957
    0.0723    3.0455
    0.1893    2.3837
    0.1344    3.0349
    0.1159    3.0462
    0.1765    2.9660
    0.1340    3.5063
    0.1504    2.5861
    0.1257    3.7062
   -0.0646    4.5121

I am not sure whats going on....

Answer 1

[Walter Roberson]

You have

X(:,1)=ones(12,1)

which creates X as having 12 rows. You then try to

X(:,2)=mgtndvi(:,2)

but mgtndvi has 13 rows, not 12.

[Justin Leung]

omg... omg... what a minor mistake... Thank you!!

[Image Analyst]

If we're done here, then please "Accept this answer".