## (“Sigma”)

Stack syntax: 'var' start end 'function' Algebraic syntax: 'Σ(var=start,end,function)'## Not in HP-28

Keyboard Access:HP48: RS-TAN HP49/50: RS-SINSummation function, also known as the Sigma function.The algebraic expression is displayed in the Equation Writer (and on the stack on the HP49/50 in Textbook Mode) as

This means “The sum of X squared, where X goes from 1 to 1000”.

The stack syntax for the same algebraic expression is:TheHP48always calculates the functionnumerically, literally looping from start to end, which can take a long time and cause round-off error accumulation. But it’s useful for small loops.The

HP49/50in exact mode interprets the functionsymbolically, simplifying many summations into much simpler forms. This yields results that are more meaningful, much quicker, and more accurate. It can also handle infinite summations (the HP48 cannot do that).Examples (for both an

HP48and anHP49/50in exact mode):0.83 seconds on HP50G; 24.4 seconds on HP48GX. exactly in 1.1 seconds on HP50G; the HP48 cannot do this one at all.BYTES: 2.5