1. Loop contains procedure call

The loop could not be parallelized since it contains a procedure call that is not MT safe. If such a loop were parallelized, multiple copies of the loop might instantiate the function call simultaneously, trample on each other's use of any variables local to that function, or trample on return values, and generally invalidate the function's purpose. If you are certain that the procedure calls in this loop are MT safe, you can direct the compiler to parallelize this loop no matter what by inserting the DOALL pragma before the body of the loop. For example, if foo is an MT-safe function call, then you can force it to be parallelized by inserting c$par DOALL:

c$par DOALL
	do 19 i = 1, n*n
			do 29 k = i, n*n
				a(i) = a(i) + x*b(k)*c(i-k)
				call foo()
29			continue
19	continue

The computer interprets the DOALL pragmas only when you compile with -parallel or -explicitpar; if you compile with -autopar, then the compiler ignores the DOALL pragmas.