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gibson:teaching:fall-2014:math445:lecture10-diary [2014/10/17 10:14] gibson |
gibson:teaching:fall-2014:math445:lecture10-diary [2014/10/17 10:23] (current) gibson |
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| We can also do the sum with a ''for'' loop. To see how to build the ''for'' loop, it's helpful to think of the series as a sequence of //partial sums// | We can also do the sum with a ''for'' loop. To see how to build the ''for'' loop, it's helpful to think of the series as a sequence of //partial sums// | ||
| \begin{eqnarray*} | \begin{eqnarray*} | ||
| - | P_1 &= 1 \\ | + | P_1 = 1 |
| - | P_2 &= 1 + \frac{1}{2^2} \\ | + | |
| - | P_3 &= 1 + \frac{1}{2^2} + \frac{1}{3^2} \\ | + | |
| \end{eqnarray*} | \end{eqnarray*} | ||
| - | The Nth partial sum $P_N$ is | ||
| \begin{eqnarray*} | \begin{eqnarray*} | ||
| - | P_N = \sum_{n=1}^{N} \frac{1}{n^2} | + | P_2 = 1 + \frac{1}{2^2} |
| \end{eqnarray*} | \end{eqnarray*} | ||
| - | Note that the difference between successive partial sums is a single term. | + | \begin{eqnarray*} |
| + | P_3 = 1 + \frac{1}{2^2} + \frac{1}{3^2} | ||
| + | \end{eqnarray*} | ||
| + | etc. Note that the difference between successive partial sums is a single term. | ||
| \begin{eqnarray*} | \begin{eqnarray*} | ||
| P_n = P_{n-1} + \frac{1}{n^2} | P_n = P_{n-1} + \frac{1}{n^2} | ||
| \end{eqnarray*} | \end{eqnarray*} | ||
| - | So we can compute the $N$ partial sum $P_N$ by successively adding the term $1/n^2$ for n going from 1 to N. | + | So we can compute the $N$th partial sum $P_N$ by successively adding the term $1/n^2$ for n going from 1 to N. |
| That's exactly we do when we compute the sum with a ''for'' loop. | That's exactly we do when we compute the sum with a ''for'' loop. | ||