Evaluate

Basic Examples

Give the antidiagonal elements of a matrix:
[◼]
Antidiagonal
[{{a,b,c},{d,e,f},{g,h,i}}]
In[]:=
{c,e,g}
Out[]=
Give antidiagonals one element above and below the leading diagonal:
[◼]
Antidiagonal
[{{a,b,c},{d,e,f},{g,h,i}},1]
In[]:=
{b,d}
Out[]=
[◼]
Antidiagonal
[{{a,b,c},{d,e,f},{g,h,i}},-1]
In[]:=
{f,h}
Out[]=
Give an antidiagonal of a nonsquare matrix:
[◼]
Antidiagonal
[{{1,2,3,4},{5,6,7,8},{9,10,11,12}}]
In[]:=
{4,7,10}
Out[]=

Properties and Relations

Antidiagonal
and
Diagonal
are related to each other:
m={{a,b,c},{d,e,f},{g,h,i}};​​
[◼]
Antidiagonal
[m]==Reverse[Diagonal[Reverse[m]]]==Diagonal[Reverse[m,2]]
In[]:=
True
Out[]=

Possible Issues

If
k
is too high or too low an empty list is returned:
[◼]
Antidiagonal
[{{a,b,c},{d,e,f},{g,h,i}},3]
In[]:=
{}
Out[]=

Neat Examples

Rotate a matrix by 45 degrees:
RowColumn
[◼]
Antidiagonal
[{{a,b,c},{d,e,f},{g,h,i}},#]&/@Range[2,-2,-1]
In[]:=
a
b
d
c
e
g
f
h
i
Out[]=