Errors in vector processing and the library libavi.a

In this paper, we describe the results of several tests that check the accuracy of numerical computation on the Cray supercomputer in vector and scalar modes. The known tests were modified to identify the critical point where roundings start causing problems. After describing the tests, we present an interval library called libavi.a. It was developed in Fortran 90 on the Cray Y-MP2E supercomputer of UFRGS-Brazil. This library makes interval mathematics accessible to the Cray supercomputers users. It works with real and complex intervals and intervals matrices and vectors. The library allows overloading of operators and functions. It is organized in four modules: real intervals, interval vectors and matrices, complex intervals, and linear algebra applications.