The DO command has the same looping function as in Fortran. The ratfor DO does not require an end-of-loop statement number, since it applies to the following statement block or line. DO commands may be nested.
DO condition statement-block
condition defines the integer looping condition which has the general form I=J,K,L. Looping is maintained provided that J<=I<=K and I is incremented by L with every pass.
statement-block specifies the statement or statements executed if the condition is true. Multiple statements must be enclosed in $( and $) braces. Note that if a statement appears on the same line as the DO condition then it must be separated by a semicolon (;).