Extensions

New features in Ratfor90 are bracketed type, subroutine, function, where, and module statements. In some ways this a further step towards the C, C++, Java model. It makes complicated modules, subroutines inside subroutines, and other advanced features of Fortran90 easier to interpret.

Ratfor90 has better error messages than Ratfor77. Besides the use of stderr, a new file (ratfor_problem) indicates where problems with interpreting programs are encountered (see Appendix C).

In many geophysical applications we perform operations of the form:

	c(i1,i2) = c(i1,i2) +  scale * e(i1,i3,i4)

Because this type type of operation is so common we borrowed from C the += and -= operators, which changes the above line into:

	c(i1,i2) +=  scale * e(i1,i3,i4)