It is iterative DO specifications connected by COMMA. specification denotes an expression or a series of expressions in this form start <TO stop> <BY increment> <WHILE(expression) | UNTIL(expression)> in this case with only the START values specified similar to DO I=1,10,20; each comma specifies a separate specification. START STOP and BY can all be expressions as in this case add two numeric constants .33+.219999 comma then another expression (a numeric constant) -1E-16 The DO iterates 2 times.
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