Wolfram Cloud Page

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[]=