## Disclaimer

The content of this blog is my personal opinion only. Although I am an employee - currently of Nvidia, in the past of other companies such as Iagination Technologies, MIPS, Intellectual Ventures, Intel, AMD, Motorola, and Gould - I reveal this only so that the reader may account for any possible bias I may have towards my employer's products. The statements I make here in no way represent my employer's position, nor am I authorized to speak on behalf of my employer. In fact, this posting may not even represent my personal opinion, since occasionally I play devil's advocate.

See http://docs.google.com/View?id=dcxddbtr_23cg5thdfj for photo credits.

## Tuesday, October 19, 2010

### Textual notation for indexed summation, etc.

I grew up with mathematical notations such as
$sum i=1,n n^i$

Now, I really believe that our programming systems should support such mathematical systems.

But seeing as most don't, I often wrestle with textural notation.

Here's a pleasant textual notation I came up with today:

first, the usual sum or sigma:
sum for i from 1 to N of A[i]

to create a vector
v[i], i=1,n
::== vector for i from 1 to N of v[i]

combining
vector for j from 1 to N of
sum for i from 1 to N of A[j+i]*B[j+N-i]

other
integral for i from 1 to N of f(i)
union for i from 1 to N of f(i)
intersection for i from 1 to N of f(i)
product for i from 1 to N of f(i)
continued fraction for i from 1 to N of f(i)
::== 1/(1+1/(f(1)+1/(1+1/f(2) + ...

2D
array
for i from 1 to M,
for j from 1 to N
of A[i,j]

3D
array
for i from 1 to N,
for j from 1 to M,
for k from 1 to L
of A[i,j,k]

shaped
array
for i from 1 to N,
for j from i to 2*i,
for k from 1 to j
of A[i,j,k]