Parallel Programming Guide for HP-UX Systems

Troubleshooting
Triangular loops
Chapter 9 191
Triangular loops
A triangular loop is a loop nest with an inner loop whose upper or lower
bound (but not both) is a function of the outer loop’s index. Examples of a
lower triangular loop and an upper triangular loop are given below. To
simplify explanations, only Fortran examples are provided in this
section.
Lower triangular loop
DO J = 1, N
DO I = J+1, N
F(I) = F(I) + ... + X(I,J) + ...
Upper triangular loop
DO J = 1, N
DO I = 1, J-1
F(I) = F(I) + ... + X(I,J) + ...
...
Elements
referenced
in array X
(shaded cells)
J
3
...
I
1
2
321