# Matrix – Meaning of ## #

While looking for an answer to a different problem, I found the following example:

``````In[1]: = Array[Plus[##] &, {2,2}]Outside[1]= {{2,3}, {3,4}}
``````

Having read the documentation of the `Space` Y `SlotSequence`, I understand the previous example. If we consider it as a matrix. $$M_ {ij}$$, take the two indexes and add them, $$M_ {ij} = i + j$$. I also understand that it is equivalent to `Training[Plus[#1,#2] &, {2, 2}]`.

I tried to make the expression a bit more complicated:

``````In[2]: = Array[Plus[##,#] &, {2,2}]Outside[2]= {{3,4}, {5,6}}
``````

that acts as $$M_ {ij} = (i + j) + i$$, or if we replace the last `#` with `# two`, $$M_ {ij} = (i + j) + j$$.

Now, I'm really stuck in the interpretation:

``````In[3]: = Array[Plus[## #] &, {2,2}]Outside[3]= {{1,2}, {4,8}}
``````

What is the corresponding expression for $$M_ {ij}$$?