# sums - COP 3502 Lab Notes Summations The CS1 portion of the...

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COP 3502 – Lab Notes Summations The CS1 portion of the foundation exam focuses primarily on algorithm analysis either through tracing the execution of code or asymptotic behavior based upon Big-Oh notation. Typically, you will see several problems where you will determine the final value produced from the execution of a code segment or possibly expressed in a summation form. This set of notes is designed to give you a look at this topic and work through some examples. Sigma notation = 10 1 i i = 1+2+3+4+5+6+7+8+9+10. The sigma (summation symbol) has a summation variable or index, i in this case, an initial value, 1 in this case, and an upper limit, 10 in this case. This expression is equivalent to starting i at 1 and incrementing it by 1 ten times and adding the value of i before each increment. Summations involving constants Start solving summations using a constant, like 3: = = + + + + = 5 1 i 15 3 3 3 3 3 3 This expression is equivalent to: 15 ) 5 4 3 2 1 ( 3 i 3 5 1 i = + + + + × = × = Constants are not part of the summation and can be removed from it. What about a case where we don’t know the upper end of the summation range? = n 1 i 3 We just saw that this was equivalent to: = × n 1 i 1 3 The question becomes: How many 1’s are there in = n 1 i 1 ? There are n of them! Summations - 1

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So the general formula for n 1 n 1 i = = Therefore, = = × = × n 1 i n 3 n 3 1 3 Summations beginning with 0 How many terms are there in the following summation? 6 1 1 1 1 1 1 1 6 0 i = + + + + + = = or, one term for each index in the range 0, 1, 2, 3, 4, 5 The general rule is: 1 n 1 n 0 i + = = since the summation has n+1 terms. So, 3 n 3 ) 1 n ( 3 1 3 n 0 i + = + × = × = Examples = 4 1 i 7 = 5 0 i 6 = n 0 i 4 + = 1 n 1 i 3 = + 5 1 i ) 3 2 ( Summations involving the summation index Now suppose that summation involves the index itself. Such as:
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sums - COP 3502 Lab Notes Summations The CS1 portion of the...

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